Since updating KDE/Plasma a few days ago, the audio output now remaps every time I switch away from my KDE desktop, and doesn't restore when switching back. The setup is a ThinkPad in a dock, with a KVM connected to the dock and the KVM connected to external speakers. The recent Audio KCM, also lists the external speakers output as "Headphones (unplugged)" for some reason, which is also a recent change. It might get confused from there being both outputs on the laptop and the dock. After switching away and back, the entire audio profile switches from "Analogue Stereo Duplex" to "Digital Stereo (HDMI 2) Output". When selecting back to "Analogue Stereo Duplex" the default output is also "Internal speakers" though speakers are connected to the external port. This used to work with KDE just using the internal speakers when the KVM was handling another computer. The last version I was running was 5.19.4
I don't see a change in 5.19 -> 5.20 that could explain this. Could it be that your PulseAudio version changed in between too?
Not sure what happened. It seems to be working again now.
Seems to have been something else being wrong for a period of time.