I was at a Genius Bar. They opened it and checked the battery, which was fine (which wasn´t a new fact for me, I used iBackupBot, full charge capacity still OK). They mentioned the not original anymore screen I replaced when killing the original one. They basically told me, to live with the FREEZES/REBOOTS because it´s pretty likely it´s the logic board. Apple does not sell them, it would be 279 € for getting a replacement device (most likely a refurbished). They also recommended to not restore the iPhone, because during this process the restore might fail and lead e. g. to an error 53 code, which means: put the device as defect on ebay.
I did a few further checks by myself like changing battery and display again to other/original hardware, also checked several connectors, removed battery health apps etc.. Didn´t make any difference, still FREEZED/REBOOTED.
Today I did, what I didn´t for a very long time - about the same period of time, the iPhone suffers from those panic.ips WDT timeout FREEZES/REBOOTS: I did an iOS update using iTunes, instead of the (much quicker, but only incremental) OTA update. Using iTunes the full operating system is replaced, not only the changed parts.
After the iOS 9.3.1 update I performed a few tests, which usually guaranteed lead to a FREEZE/REBOOT, like e. g. performing app updates. I collected them the last days, 18 updates without a problem. At the beginning it "soft-freezed" (clock didn´t change for a few minutes), but the hardware was functional (like e. g. working display brightness sensor or still playing music), it ended with "apps can´t be loaded at the moment" message. Performed the updates again, finish. iOS now managed to NOT run into a timeout ("WDT timeout"), there was no REBOOT, no panic.ips. So I guess it was a defect system file/setting, which was replaced by an original/not defect.
I´ll monitor this closely the next days and weeks, but for the first time after 15 months I´m really confident.
To all the others still suffering from the same: It MIGHT be worth a try (iOS update using iTunes). Did you also perform the iOS updates always via OTA? panic.ips seems to has several reasons, so there´s no guarantee it will work - maybe just give it a try (after performing an iTunes backup of course).
