no audio output from B4 II (intermittent)

[daver59]

Here's a strange one:
Have been happily programming multis for a couple of weeks without issue. Then yesterday after practicing for a bit I stepped out and left the system on - but when I came back a few hours later the B4 II part of the multi had just stopped working. Thought it was a MIDI issue but the 'Manual' tab in the VST is showing notes when I hit the keys and if I reassign that MIDI channel to a different VST it works fine. Nothing muted in the Mix and reloading the multi doesn't work. Only rebooting seems to fix the problem and even then it seems to mute itself after a while. Sound familiar to anyone?