No audio when starting and accepting a phone call

Mobian: Trixie Device: OnePlus 6 and OnePlus 6t

When I start a phone call (test call via Echo service) and then switch back and forth between devices in the audio settings, I can eventually hear myself. This means that the audio input and output as well as the modem are working. However, I have to do this again for every call. When a call comes in, I can't hear anything and the other person can't hear me either.

Is there currently a workaround for this? It seems to be only related to the routing of the audio streams.

I have already tried all the workarounds listed at https://wiki.debian.org/InstallingDebianOn/OnePlus/OnePlus6#Audio.