iPhone 17 Pro Max iPhone 17 (Pro / Pro Max) – Cellular modem fails to recover after signal loss (reproducible, persists through iOS 26.2)

[kawa636r]

I’d like to report and compare notes on a reproducible cellular issue I’ve been able to document on the iPhone 17 series, which has persisted across multiple iOS versions up to 26.2.

This is not a signal coverage complaint, and I’m not talking about temporary slowdowns. This is a failure to recover cellular service after complete signal loss.

Reproduction scenario

This occurs under very normal real-world conditions:

1. Device is on 5G Auto
2. Enter an area with complete signal loss (e.g. basement / underground parking)
3. Device correctly shows No Service
4. Return to an area with known good coverage
5. Device does NOT recover service
6. Cellular remains unusable indefinitely until Airplane Mode is toggled

At no point does it self-recover.

Key observations

Using Field Test Mode (*3001#12345#*):

• The phone often remains logically attached to an LTE cell
• RSRP and RSRQ return to good values
• SINR values become impossible or extreme (e.g. –18 dB, –30 dB, sometimes even one RX chain reporting ~ –40 dB)
• Status bar may still show No Service or frozen connectivity

Only a manual baseband reset (Airplane Mode) restores service.


Why this appears to be a modem / firmware issue?

• The issue is 100% reproducible once triggered
• It persists across iOS versions (tested up to 26.2)
• It occurs even when signal conditions are objectively good
• A second iPhone 17 tested side by side may recover normally, suggesting a latent state-machine issue rather than coverage or carrier problems
• LTE-only mode greatly reduces the likelihood of hitting the bug

This strongly points to a baseband recovery / re-attach failure after total signal loss, likely related to state handling during handover or reacquisition.


What this is NOT

• Not carrier specific (tested with Movistar; behavior consistent across environments)
• Not SIM / eSIM related
• Not a “weak signal” issue
• Not fixed by resets, network settings, or reinstalling iOS

Why I’m posting


I’m not looking for troubleshooting tips or a device replacement discussion.


I want to know:

• Are other iPhone 17 / 17 Pro / 17 Pro Max users seeing the same behavior?
• Especially users who frequently move between no-signal → signal environments
• Has anyone seen improvement in 26.2 or later?

Given that this affects core cellular reliability, I believe it deserves visibility and confirmation.

Suggested test for others

• Enable 5G Auto
• Enter a location with total signal loss
• Return to coverage
• Do not toggle Airplane Mode
• Check Field Test SINR values

If the phone stays offline until manually reset, that’s the issue.

Looking forward to hearing if others can reproduce this.


If enough people are seeing it, it may help get this in front of the right engineering teams.

 

[jz0309]

I’d like to report and compare notes on a reproducible cellular issue I’ve been able to document on the iPhone 17 series, which has persisted across multiple iOS versions up to 26.2.

This is not a signal coverage complaint, and I’m not talking about temporary slowdowns. This is a failure to recover cellular service after complete signal loss.

Reproduction scenario

This occurs under very normal real-world conditions:

1. Device is on 5G Auto
2. Enter an area with complete signal loss (e.g. basement / underground parking)
3. Device correctly shows No Service
4. Return to an area with known good coverage
5. Device does NOT recover service
6. Cellular remains unusable indefinitely until Airplane Mode is toggled

At no point does it self-recover.

Key observations

Using Field Test Mode (*3001#12345#*):

• The phone often remains logically attached to an LTE cell
• RSRP and RSRQ return to good values
• SINR values become impossible or extreme (e.g. –18 dB, –30 dB, sometimes even one RX chain reporting ~ –40 dB)
• Status bar may still show No Service or frozen connectivity

Only a manual baseband reset (Airplane Mode) restores service.


Why this appears to be a modem / firmware issue?

• The issue is 100% reproducible once triggered
• It persists across iOS versions (tested up to 26.2)
• It occurs even when signal conditions are objectively good
• A second iPhone 17 tested side by side may recover normally, suggesting a latent state-machine issue rather than coverage or carrier problems
• LTE-only mode greatly reduces the likelihood of hitting the bug

This strongly points to a baseband recovery / re-attach failure after total signal loss, likely related to state handling during handover or reacquisition.


What this is NOT

• Not carrier specific (tested with Movistar; behavior consistent across environments)
• Not SIM / eSIM related
• Not a “weak signal” issue
• Not fixed by resets, network settings, or reinstalling iOS

Why I’m posting


I’m not looking for troubleshooting tips or a device replacement discussion.


I want to know:

• Are other iPhone 17 / 17 Pro / 17 Pro Max users seeing the same behavior?
• Especially users who frequently move between no-signal → signal environments
• Has anyone seen improvement in 26.2 or later?

Given that this affects core cellular reliability, I believe it deserves visibility and confirmation.

Suggested test for others

• Enable 5G Auto
• Enter a location with total signal loss
• Return to coverage
• Do not toggle Airplane Mode
• Check Field Test SINR values

If the phone stays offline until manually reset, that’s the issue.

Looking forward to hearing if others can reproduce this.


If enough people are seeing it, it may help get this in front of the right engineering teams.

had my 17PM since launch, had a few occasions where I was in a "dead zone" with "No signal" showing, reconnected every time I was back in a covered area, not that I was monitoring this, I just did not have an issue. I'm in the US on TMobile.
You seem convinced it is not carrier related, and also it seems like you are on beta? Have you been able to reproduce this on the released OS version? Have you contacted Apple about this?

 

[kawa636r]

had my 17PM since launch, had a few occasions where I was in a "dead zone" with "No signal" showing, reconnected every time I was back in a covered area, not that I was monitoring this, I just did not have an issue. I'm in the US on TMobile.
You seem convinced it is not carrier related, and also it seems like you are on beta? Have you been able to reproduce this on the released OS version? Have you contacted Apple about this?

yes, since day one on all the firmwares.

i have wrote apple on feedback app and directly on tim cook email, to see if someone is able to escalate this to engineering team.

 

[TheIntruder]

Whatever behavior that's been observed is not universal.

On a recent trip, I surprisingly found myself with "SOS" displayed more than once in the middle of a dense metropolis. Indicating no connection to cell service of any kind.

26.1 on the AT&T 5G network in the U.S.

Each time, signal recovered on its own after moving out of the dead zone.

 

[kawa636r]

My test was done in Spain, with Movistar, Digi and Orange ISP, and it's easily replicable. Wifi calling was enabled by the way

 

[Cobalt Blizzard]

Something like this happened to me once. Phone got stuck on EDGE after entering area with a poor signal and won't switch back to 4G or 5G unless I manually toggle airplane mode ON and OFF.

 

[kawa636r]

looking reddit it seems there are many first day iPhones that had a slightly defective modem. I'll ask for a replacement and look for the situation.

 

[kawa636r]

Update – Incoming calls not delivered while device appears attached to LTE​

Quick update with an important additional symptom I’ve now been able to document.
While the device is in the failed state (after losing signal and re-entering coverage, without toggling Airplane Mode):

• Field Test Mode shows:
  
  • Valid LTE cell (PCI / Cell ID present)
  • RSRP around –110 to –112 dBm
  • RSRQ around –7 dB
  • SINR degraded (–15 to –20 dB), but not zero
• The phone may still show No Service or frozen connectivity

However, when someone calls my number during this state:

• The caller hears normal ringing tones
• The network clearly treats the device as reachable
• The iPhone does not receive the call at all
  
  • no ringing
  • no UI notification
  • no missed call entry after recovery

In other words, the device appears to be registered on the network but fails to respond to paging until the baseband is manually reset via Airplane Mode.

This goes beyond “poor signal” and points to an attached-but-unreachable modem state, which explains why calls can be silently missed even when LTE metrics look reasonable.

Still seeing this behavior on iOS 26.2.

If anyone else is testing this, pay attention not only to data recovery, but also whether incoming calls are actually delivered after returning from a no-signal area.

 

[kawa636r]

Final update – Issue reproduced on replacement device with strong signal​

Final update to close the loop on this thread.

I can now confirm that the same cellular failure has been reproduced on a replacement iPhone 17 Pro, and this time under clearly good signal conditions, which removes any remaining ambiguity.

---

Observed state​

On the replacement iPhone 17 Pro, in a known coverage area:

Field Test Mode shows:

• LTE active
• Band 3
• Valid PCI and Cell ID
• RSRP: –92 dBm (strong signal)
• RSRQ: –6 dB (excellent quality)
• SINR: ~ –9 to –10 dB (marginal but usable)

Despite these values:

• The device remains in “No Service”
• Cellular data is unavailable
• Incoming calls are not delivered
• Toggling Airplane Mode immediately restores service

This is not a weak-signal or edge-of-coverage scenario. With these RF metrics, the device should be fully operational.

---

Additional critical symptom​

When the device is in this state:

• Callers hear normal ringing tones
• The network treats the device as reachable
• The iPhone does not receive the incoming call
  
  • no ringing
  • no notification
  • no missed call log after recovery

This indicates the device is registered/attached but unreachable, i.e. it fails to respond to paging until the baseband is manually reset.

---

Conclusion​

At this point the pattern is clear:

• Reproducible on multiple iPhone 17 units
• Persists across multiple iOS versions (tested through 26.2)
• Occurs after loss of signal and return to coverage
• Can manifest even with strong LTE signal
• Affects incoming call delivery
• Recovers only via manual baseband reset

This is consistent with a cellular modem recovery/state-machine bug, not a carrier issue, SIM issue, or general “poor reception”.

---

Why I’m posting this update​

Not to seek troubleshooting advice or debate return policies, but to document the issue clearly in case:

• Other users are experiencing silent missed calls
• Engineers or technically inclined users want a reproducible scenario
• This needs broader visibility beyond isolated reports

If anyone else tests this, please pay attention not only to data recovery but also to whether incoming calls are actually delivered after returning from a no-signal area.


Thanks to everyone who followed along or compared notes.

 

[kawa636r]

Update – potential security impact, reported to Apple Security​

Posting an important update to this thread.

While investigating the cellular failure described above, I’ve identified a potential security-relevant scenario related to the issue, which I have now reported to Apple through the Security Research program in parallel to standard bug reporting.
In short:

• The modem can enter a persistent “No Service” or unreachable state after specific connectivity transitions (notably involving Wi-Fi Calling).
• In this state, callers hear normal ringing tones and SMS are reported as delivered, but the iPhone never receives calls or messages.
• The user is often unaware the device is unreachable until manually resetting the baseband (Airplane Mode).

This creates a silent denial-of-service condition affecting calls and SMS, including notification or verification messages.

I’m not claiming an exploit chain or data access, but there is a clear availability and safety concern, especially if the condition can be repeatedly triggered in specific environments without the user noticing.

The issue has been documented with logs and reproduction steps and submitted to Apple via:

• Feedback Assistant (telephony / baseband)
• Apple Security Research (as a potential availability vulnerability)

I’ll avoid posting further technical details publicly and will update only if Apple provides guidance or resolution.


If others notice missed calls or SMS while the phone appears reachable or callers hear ringing, please pay close attention — this may be related.