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macrumors regular
Original poster
Oct 3, 2012
Orlando FL
WARNING – The latest security updates for both 10.14 & 10.15 may disable the inner-most usb-c/thunderbolt port on iMac Pros. I have two Macs with the same issue. One on each OS. The 2nd mac was working fine until the update was installed, then the port was disabled; pointing directly to the security updates as the culprit. A T5 SSD connected to this specific port shows no power light. The same result appears on both affected Macs.

This is the port next to the ethernet port on the iMac Pro. Radar has been filed : FB7639274
Last edited:


macrumors 6502a
Mar 12, 2011
Lansdale, PA, USA
I saw the same with the current security update tonight. Secondary monitor was not on after install on 10.14. I just pulled the thunderbolt cable and plugged in again. The monitor came and went several times, then finally settled in to working again. Very odd.


macrumors newbie
Apr 2, 2020
I tried disconnecting and then reconnecting the adapter to my computer and nothing happened.

What DID work was unplugging my display from the electrical outlet and then plugging it back in.

Hope that helps anyone also experiencing this issue.


macrumors member
Oct 17, 2018
The issue appears not only with the Catalina update but also with security update 002 for Mojave. Several computer models seems to be affected.
SMC reset does not always help.
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