Same for me - and thanks for the suggestion! My FP3 had worked for years without problems (in contrast to the previous FP2, which had suffered from the Random-Reboot-bug). Then I decided to upgrade the camera module. Swapping the module itself was no big issue, but afterwards, I got either:
a rainbow pixel screen (with losely tightened screws),
a black screen (for really tightenend screws).
(In both cases, the phone still reacted to switching it on.) Dis- and reassambling, twisting etc. did not help, but cleaning the golden contacts with isopropanol (from a well-equipped pharmacy) and a cotton bud removed the problem. Fortunately, the phone is fine again.
I had the same issues with a newly bought screen. Reassembling the screen did not work (actually it made it worse). Even loosening the screws or tightening the screws. Usually, a hard press or a twisting of the phone fixed it. But only temporarily.
What fixed it for me, was to take some very fine sand-paper and gently applying it to the pogo-sticks and the contacts. I assume that some oxidation layer had formed on the contacts or pogo sticks which made the connection flaky. It has been working for a few days now with no issues (even after i dropped the phone on a tiled floor).
I bought a FP3+ off ebay with a known display issue (noise, coloured lines, etc.), but in otherwise perfect condition. Cleaning it up the contacts didn’t help at all so I bought a new display module. The bootloader warning and fairphone splash work fine but as soon as Android starts loading I end up with the display freezing/super-slow and/or noise issue. I’ve tried most of the suggestions on here (including some of the more dubious, which for all I know made things worse).
The odd thing is it seems to be most reliable if I don’t put any of the screws in - if I do it is a seemingly random loosening and tightening that will find a sweet spot that lasts at most an hour, or immediately stop working if I put the back cover on. If I leave the screws off I can put the back cover on and the “twisting” technique to fix the phone seems to work (which isn’t the case with the screws in).
My suspicion based on the above is a short circuit of some sort rather than a loose connection, but I’m perhaps grasping at straws.
Does anybody have any suggestions? Sadly so far this phone is proving less reliable than the one it is replacing (and that is saying something).
My FP3 had worked for years without problems (in contrast to the previous FP2, which had suffered from the Random-Reboot-bug). Then I decided to upgrade the camera module. Swapping the module itself was no big issue, but afterwards, I got either: