I have progress but not complete success yet, and some important info that I originally thought might not be important.
This started with a shot of Fireball getting kicked onto the unit. Wiped it off at the gig, didn't seem like a lot of liquid but it probably got in around the displays and maybe footswitches. (This was near the end of the night and the unit kept working through the last couple of songs).
At home the following day when it didn't work right, I opened it and discovered the disconnected ribbon cable (possibly caused by my singer shaking the unit after wiping it) and assumed that was my actual/ only issue.
After posting this I did notice sticky areas and in addition to your 2nd ribbon cable suggestion I cleaned the boards and the displays with isopropyl (once or twice over with a soaked toothbrush) and let it dry for a day. Today the displays are working again and I thought I was all good but it's still stuck in a boot loop.
I tried a reset (tap +6) and another force update using line 6 updater. It updated to 3.8 but still keeps rebooting.
I think I'll try to clean it more thoroughly (also will use 99%, this was 91%).
AI suggests I may be screwed at this point (component fried) but it's worth a try.