I had the same issues but only a few times, luckily. I never saw it in the last… let’s say… couple of months.
When it happened, it looked like the microphone stopped working. WhatsApp audio messages were empty, videos were silent and the voice recorder also recorded empty audios. I had to reboot to solve the issue.
It started after updating to Android 11, I’m now at build number “8901.4.A.0013.4 release-keys” (I don’t know what that “release-keys” is about but it’s in the “Build number” string).
I have an SD card and it’s not configured as internal memory.
Please let us know if support finds you a solution.
Ciao,
Max