Hi and welcome to the forum.
Just to clarify, this is user forum, so no official response can be expected.
Of course you can try installing the FOS to see if it is an e/OS issue…
Where are you? You may find a fairphoneangel near you that can lend you a top module to test that idea.
https://angels.fairphone.community/
You may also try removing the top module and doing a clean etc.