Thanks,

Don't have the Creator's Update installed (yet). But I'll keep this in mind.

PG music thinks it might be some kind of interaction with the external MIDI and/or Mixer drivers, but since the latest Win10 update the problem has gone into hiding, so it is likely that M$oft broke something in the previous update that got fixed.

Or it's just trying to lull me into a false sense of security:)

Time will tell.