bluetooth audio under pipewire: playback silent?

Hi list,

I am (still) trying to get audio playback to a bluetooth speaker to work
with pipewire. Having succeeded a single time, my bluetooth speaker
now remains silent when playing back over pipewire: 

Playback is audible when addressed via (blue)alsa as
	aplay -D bluealsa sound.wav

But not via
	aplay -D pipewire sound.wav
	
The bluetooth speaker is set as pipewire's default audio sink with
volume 0.8 and not muted as verified with alsamixer or
	wpctl status
qwpgraph shows a connection between aplay and that speaker, as does
	pw-top
yielding
R   71   2048  48000 152.0us  79.6us  0.00  0.00    0     S16LE 1 8000 bluez_output.30_C0_1B_C2_B6_D3.1
R   65   5512  44100  33.0us  97.3us  0.00  0.00    0    S16LE 1 44100 + alsa_playback.aplay

I can even hear a short click in the speaker when playback starts, but
no audio signal. There are no messages in journalctl -efx.

pavuctl shows a headset unit HSP/HFP profile with CVSD codec for the bluetooth
speaker.

Restarting pipewire does not help:
	systemctl --user restart wireplumber pipewire pipewire-pulse

I am clueless what to try next, all help is greatly appreciated!

cheersz, Peter