PW->usb-midi out often doesn't work

I tried this with c8fd34a4 on two different machines.

One is running the session with ./pw-uninstalled.sh and make run the receiving usb device gets midi. The other is running a system-wide session with systemd service and socket, the receiving usb device does not get midi.

After this initial test I went back to the machine where things where working (with make run), however now I cannot get midi-to-usb to work any more.

Any midi handling within pipewire is fine (ie alsa-midi to pw-jack carla is received correctly). alsa-midi to usb-output is rarely hit and mostly miss