[24.04-1.x] a-i-sound, Music app/qtubuntu-media can't find media-hub-exported MPRIS

Symptom: while playing a song in Music app:

• a-i-sound can't find MPRIS at all and act as if there's no media playing.
• Music app itself doesn't show "cover art", and the track name is shown as file name instead.

This is weird, because I do see org.mpris.MediaPlayer2.MediaHub exported on session/user DBus.