... and then I reboot and that fixed it.

Hopefully for us this thread doesn't get many posts, but I seem to recall once or twice people said " and then I power cycled the GM and it fixed the problem".  It might be interesting to see if there are any trends with this device.

I don't recall having to reboot the gm before, but last night during sound check my sound was dropping out occasionally - like for about 1/2 second every few seconds (but it was not cyclical).  I did the usual bypassing my wireless, then pedalboard, then plugged straight into the gm, it was the culprit.  PANIC!.  Powered it off for 5 seconds, and the problem never occurred again.    

Have you ever had to reboot your GM?

Excellent thought for a threqad Namklak.

Yes I have had to reboot but not for anything like your own reason. Very early on I had a single EL84 go mental on me at switch on. It's usual to see valves with a slight blue glow around them in use, (not good but fairly common). I had one glow cherry red! And that certainly isn't good for the valve. I still have no real idea what caused it, I put it down to the active bias control in the GM sneezing. After quickly switching off and tentatively rebooting while I held my breath it was fine and I haven't seen it since. It seemed to do no damage to the valve, it lasted the same time as the others before replacement.

I suspect there may be a few more posts here before too long. The mix of digital control over analogue circuitry is always open to this sort of problem.