Chosen Solution
Phone keeps restarting after around 3 minutes. Customer came in for charging port replacement. All screws in right place, no long screw damage.
It has had the following to rule out:
Battery and 3 replacement ports. Each flex cable was unplugged one by one to troubleshoot, even with the following unplugged it occurs: Screen Flex (Both), Face ID/Front Cam Flex (All 3), Antenna Flex (Wifi), Lower Antenna, Power Button Flex/Flash & Volume Button Flex & Charging Flex.
I have tried a replacement screen and still occurs. I have checked all the FPC under microscope and very clean and tidy. It cannot be the port surely as it occurs even when not plugged in.
Assuming it was working fine prior to your repair attempt, then I would take a closer look at the small components surrounding the connectors. If you see anything dislodged or damaged, then that would probably cause your issue. At this point, you may need to have this looked at by an experienced micro-solderer.
So apparently after some investigation, this appears to be an issue with 3rd party charge port cables. Apparently in iOS 13+, there is software that monitors thermal readings from the charge port modules and the 3rd party cables do not allow this to happen which triggers a kernel panic, restarting the phone.
