Every third phone call is completely silent for both parties

I have a 2 year old Samsung Galaxy C9 Pro that runs on Android 8. I tried doing a hard reset, running the phone in safe mode and using a different SIM card and the problem persisted regardless. It also happens regardless of whether I'm the one making the call or receiving it and regardless of whether the call is on speaker or not. I tried going to the apps list to clear the data from the Phone app but it weirdly didn't appear on the list. This, and the fact that everything works completely fine 66,66% of the time makes me think this is a software-related issue.