Did you dirty flashed the beta a12?
Had yhe same issue...clean flash did the trick
Nope, not gone near the beta yet. I have flashed back to complete stock now on VOD CSC (3AUHD), with only Magisk added for root. And it still does it. I also changed my SIM to an eSim to rule out the sim card or the sim card reader, but it made no difference, I still had silent calls after a day or two.
But I'm wondering if Afwall+ was stopping a service required on the newer builds, as I always have it blocking all apps including system apps, unless access to data is a requirement for the app to work. So I have now disabled the firewall. Also, as indicated above, I've installed Google's dialler app for both incoming and outgoing calls. I would have thought the fact a reboot fixes the issue each time means it's not a hardware fault. I'd hope so anyway.
It's clearly not this build anyway, so I can flash it back on my phone.