There is no overlap in your settings and boot config is also ok, I can’t see if you have marked jack instead of HDMI but you have told Heiner that you did.
Normally when we talk about software errors its more black or white (either it works or it doesn’t) It is more likely some outer interference ….. like your power supply (we are all hav’ing that problem sooner or later) I wood suggest that the next thing to try is the minimalistic approach. uninstall bluetooth and unplug your usb sound card. If you have other usb / GPIO devices pluged in remove them too.
maybe if load all on one PI and nothing on the other … does that make a difference ???
Most 5v plugs are more likely 4.6-4.75v wich is too low for the PI.
Let me know the result of your test, I will try to think of any other possible solution.