Hi and welcome.
UPDATE
Sorry didn’t notice it’s an FP4 not an FP3 but you can still use the links to help get the FP4 versions.
As the phone is modular it can happen that contacts between modules work loose with the best of care.
Read the iFixIt detail on how to disassemble and resssemble. You can also check for damp etc. whilst doing so. ( Third link )
Read the ifixit then the official Fariphone way of removing the screen
Do not go past step 7 if you follow the iFixIt guide, up till then you do not void the warranty.
All the best