I started in safe mode and the issue is gone. Now I have to figure out which &%#&@) app is causing the issue. After rebooting the phone out of safe mode I started uninstalling recent apps and that so far has not solved the issue
I can also confirm this bug, except it also seems to happen when disconnecting from ANY bluetooth device, in my case, my smartwatch. The watch was in the other room and was connecting/disconnecting every few minutes. While I was on a call the audio kept switching to speakerphone during this time. Really frustrating, and as someone else pointed out, quite a big security risk.