@Sietse
This is going in a loop. This has been suggested already :
_ October 2019 No sound 50+% of the time in calls, until reboot - #4 by NicoM
_ December 2019 No sound 50+% of the time in calls, until reboot - #6 by matthewbednarski
_ September 2020 No sound 50+% of the time in calls, until reboot - #62 by hans.stoops
With a 2 min quick search of the word “SIM” on that very topic, this loop is actually the third iteration about suspecting the SIM. I might have missed another iteration.
To anyone reading that post, you should :
_ Open a ticket as soon as possible.
_ Do consider getting reimbursed before they fine some sketchy reason not to (Group action against Fairphone for dishonest support on Fairphone 3 - #26 by BertG). Weight how much you want a Fairphone. The coolness fades away but the need of a working phone doesn’t.
_ Ask over and over to get the phone swapped. It is not up to you to prove that it is a HW problem. Fairphone has now failed to solve that problem with ALL updates since Fairphone 3 came out, that is 3 updates if I remember well. And now 16 month + since Fairphone 3 is out. Meanwhile, some users do not report having a problem. Why should some be lucky and other not. This is not a lottery, but a company selling phones. Consumer law exist for a reason.