Instrument track doesn't play after unmute

There's midi notes arriving in the Soft Synth.
There's audio in the FX of that Soft Synth.
There's no audio on the channel or the master.
 
Tried toggling everything, mute on / off, input echo all states, FX on / off.
Tried freezing the track. The frozen clip contains visible audio, but it doesn't play. If I copy the frozen clip to a new audio track it plays.
 
Please clarify what setting is wrong or if it's a bug.
 

 
Thanks.