[com.android.dialer] Unreliable Phone Calls on 18.1-20210906

Affected app
Name: [Phone]
Package id: [com.android.dialer]

Describe the bug
Incoming and outgoing phone calls are unreliable in this build (20210906).

To Reproduce
Steps to reproduce the behavior:

1. Use the device as a phone...
2. Notice phone calls are unreliable

Expected behavior
Incoming calls either get dropped or the other end cannot hear audio, particularly on Skype meeting calls. Outgoing calls, e.g. voicemail, fail to connect. Particularly bad on 20210906-microg; previous build was better, but suffered from this bug.

Screenshots
If applicable, add screenshots to help explain your problem.

System
Android Version: [e.g. 11]
Custom ROM: [LineageOS 18.1-20210906-microg]

microG
microG Core version: [0.2.22.212658]
microG Self-Check results: [All ticked]

Additional context
Adding two bugreports + logcats.
bugreport-shamu-RQ3A.210805.001.A1-2021-09-07-13-31-33.zip
bugreport-shamu-RQ3A.210805.001.A1-2021-09-10-14-51-20.zip

Start with the two attached bugreports and logcats for the 20210906-microg build, using the com.android.dialer package and the previous-build comparison as context. Trace the evidence for dropped calls, missing audio, and failed outgoing calls; done means the responsible regression is identified and phone-call behavior is verified as reliable.