"Parasitic cellular data drain" iPhone XS after iOS 18.x installed

[robbinia]

On July 7th I did a clean re-install of iOS 18.5 and then updated to the dev beta 3 of iOS 26 and since then the consumption of cell data has been really low. I started iOS 26 with none of my apps installed except My Data Manager and had nothing running for a few days then gradually reinstalled my apps and switched on location services, etc. It's used 192mb of cell data for system services since the update (avg 15mb/day) which is a massive drop compared to how it was on iOS 18.

For the past few days it's been back running as a 'normal' iphone & I'll definitely be updating to the public beta of 26 if/when it comes out this week as it seems way better running the new iOS (even in beta form) than 18.

 

[Newtons]

It’s bad enough all these tech companies make a lot of money from selling our data.

I hope they aren’t wasting our data somehow to spy on us, and then making us pay for the data consumption (minus the unlimited data plans)

 

[Neebee]

I can't believe the issue still isn't "recognized" by Apple. Just today I got hit with 120 MB+ drain after enabling cellular data. Sometimes, I can go for hours without the drain. The trigger seems to be whenever the iPhone "calls home". It sucks there's not much info online but I get it. Most people have insane amounts of data so it's not an issue. But if you're using a travel eSIM you need to pay more for a higher data bucket.

 

[Neebee]

On July 7th I did a clean re-install of iOS 18.5 and then updated to the dev beta 3 of iOS 26 and since then the consumption of cell data has been really low. I started iOS 26 with none of my apps installed except My Data Manager and had nothing running for a few days then gradually reinstalled my apps and switched on location services, etc. It's used 192mb of cell data for system services since the update (avg 15mb/day) which is a massive drop compared to how it was on iOS 18.

For the past few days it's been back running as a 'normal' iphone & I'll definitely be updating to the public beta of 26 if/when it comes out this week as it seems way better running the new iOS (even in beta form) than 18.

It's bizarre. My spouse's iPhone 13 has no issue and the settings aren't as conservative as mine. My XS can't upgrade to iOS 26. My guess is Apple doesn't care about us who have unsupported phones like the XS.

 

[ManuCH]

Honestly, you use a museum phone and you are on some plan from the 1980s. Maybe you should get an Android 😉

 

[colin773]

I came here to thank OP because I've been wrestling with the same issue for ages. It's not a carrier bug. It's not OP's old phone. OP isn't imagining it. My own issue, which fits OP's description exactly, cost me $90 in fees last month for exceeding my data plan. Unlimited plans don't make sense for all users on all carrier networks, and for people like me and OP, this issue is a serious problem.

I've been to the Apple Store twice to present my own detailed findings while troubleshooting this, only to stump the Support supervisor/head "Genius" and be told there's nothing else they can do for me. I would reach out to Apple Support by chat or phone, but OP's own experience doesn't inspire much confidence.

The steps OP shared from their own troubleshooting and the deleted Reddit post have been helpful to me so far in identifying updates.cdn-apple.com as the main culprit in my own runaway data use. I only blocked it moments ago using Proxyman, so it remains to be seen if it's totally effective in solving my issue. I anticipate it will be and plan to report back here.