Device Will not Boot Fully with Replacement Screen

I am repairing an iPhone 6 for a customer. Some context is needed for this question: The iPhone had some water spilled on it, and then would not power on. I reseated the battery, and the phone started booting just fine, but the home button didn't work. I replaced the home button, and the problem appeared to be solved for about an hour, but then the replacement home button stopped responding as well.

(Note: I also updated the software somewhere in there, but I don't remember where exactly. I think I may have done that in order to get the phone to boot fully, but can't remember.)

I thought that was odd, so I decided to replace the display and test with the original home button again. Home button works (I know because the phone responds to resets), but the phone will no longer boot fully. It powers on to the Apple logo, but then goes to a blank black screen (with backlight still on) and reboots. I put in the replacement home button once more. That button works as well, but phone still won't boot.