U3421WE, audio issues

I am experiencing some strange audio issues with my U3421WE. I believe it's really some serious mess up with how it deals with the USB hub, esp. when when switching devices connected to the monitor. 

It's mainly connected to a 2020 Macbook Pro 16" via USB-C as my business setup. I use it a lot with Teams. In addition a Logitech Mouse and Webcam are connected to the USB hub from the monitor (I no longer use the hub's Ethernet port as it brought a lot of other issues.).

It all works for quite a while as it should, with audio being delivered by the internal speakers, everything ok incl. sound level control. However as soon as I attach another device only once to the monitor (sometimes my son uses it with his MBP when visiting us), or switching input port to HDMI for a rather rarely used PC (incl. switching USB hub for mouse, cam and keyboard), audio is going crazy afterwards when switching back to Mac. It's one of always these same issues: no audio whatsoever, too loud or too low audio with no way of changing it (via monitor menu or DDC) or only one channel working (usually the right, with left being off). And there is only one single way of fixing it again: unwire the monitor overnight. Less than 5 hours break won't do (just potentially toggle symptoms as mentioned above). After a night of "rest", it will come back to normal for my Mac. Everything Dell wants to fix with audio issues pertains ALWAYS to some audio driver stuff on the PC, which doesn't even apply here. Also, the symptoms are the same whatever device I hook up then, so it's "in the monitor", not any driver issue. I believe it's some kind of messed up USB electronics that only settles when unwired for multiple hours. I'd wish there was just some simple way to reset the USB hub to it's base state to avoid this procedure, because it always means that my monitor is normally usable for me only the next day then.

I had my first very same monitor exchanged already for the same symptoms, but this one has the same behaviour, so it appears to be rather a systematic issue. Also after updating to latest firmware, nothing changed (other than the span of possible volume control is now better than it was with previous firmware, so I can control a larger volume range altogether...)

Does anyone have any clue what other easier procedure could help here to get USB sound going again normally? Dell support is of no help here, being totally focussed on PC driver stuff only for such kind of problems.