I have this problem too and it seems quite a common fault with FairPhones, the display contacts just aren’t up to the job and never have been in any generation of the phone. I’ve had my phone - FP3+ - about 8 months and so far I’ve sent it back to be repaired once and repaired it twice myself by taking the screen off and cleaning the contacts. Other threads on this topic are:
https://forum.fairphone.com/t/coloured-pixels-screen/81908
https://forum.fairphone.com/t/rainbow-pixelised-screen/55995
https://forum.fairphone.com/t/fp3-display-freezes-display-noise-issue/55277
There are probably more, this really is a major flaw in the design.
My phone is showing the same fault again so I’m coming up to my 4th dismantling in less than a year. This is not good. Has anyone come up with a fix for this problem that lasts longer than 2 months? I’m also aware that the display retention screws go into plastic, so will wear out, I expect the fault will become unfixable after a few more goes round because the screws won’t hold any more.