Hello,
I use kde for several years, and i really prefer it over the other DE. However there is a very annoying bug that i have for several years. I use a Soekris dam1941 dac with it's usb interface.
There is two "side" of the problem. First if i power on the dac before starting my computer, it get recognize well. However if i am in kde desktop and power on the dac, it is very often not recognize and i need to unplug - plug again the usb cable.
Secondly the dac stop working randomly, it's not recognize anymore and i get the kde volume control icon telling me it switch to another peripheral. It is totally random, sometimes the problem occur when i am on the desktop without any sound playing, or sometimes it make app to crash. Often when i start playing a video mpv just hang and crash and i see the dac disconnecting. Problem is not from my DAC, i made some test and the problem only occur in kde, not in other DE or windows. So i suppose this problem is specific with phonon.
Strangely when the dac is like disconnected, i still see it with lsusb command, but it's like it disappear in the volume manager or kde multimedia settings.
In this case i also need to unplug and plug again the usb to have the dac to work again. It's annoying really,
Another thing, i also own a soekris dac1101 that is the portable version also with a usb inferface. Problem is the same, so i am sure it's not a problem only with my dam1941, and the same problem with surelly occur with all soekris dac with their built in usb inferface. Apparently soekris is using the "Thesycon USB driver" :
"The dam1941 also include a license for the full Thesycon USB driver set"
So it's most likely the problem will occur with other dac with the same usb interface.

If no one care please at least tell me where i can open a bug report for this...

Ideally to your distribution, as not all ship the same phonon branch.