iPhone 6 getting very hot and turning off during boot after screen replacement

Firstly, Hi GSM-Forum. I’ve lurked for a long time but never posted — so thanks for all the help you’ve already provided.

I have an iPhone 6 that is giving me some big issues, I’ll simply list all known informaiton:

Phone was dropped several times, cracking the screen.
Phone was in great shape before a front assembly swap.
Assembly was swapped with the power on.
No tools were used and the LCD was off during the swap.
Phone needed to be rebooted to turn on after the repair.
Upon reboot the phone worked while testing functionality until it suddenly went black, gave the swirly circle and powered down — the back portion behind the board was quite warm.
The phone then said the battery was dead.
I plugged in a charger and the phone rebooted with ~25% battery.
The phone made it to the home screen and turned off again after about 10 seconds.
The phone now will not make it to the home screen when booting before it turns off.
The phone boot loops when a charger is plugged in with no battery plugged in.
The shield above the A8 processor gets very warm when attempting to boot.
The back of the phone, beneath the processor also gets very warm during boot.

I’ve tried all of the basic repair ideas (different glass, OEM glass, different small parts, different charge port/battery, etc.).

Does anyone have any thoughts on what the issue could be? Is it the power management IC?

Thank you for the read and for any help, I hope to provide the community with answers in the future as well.