first time I hear of such a problem.
My guess is that there is a bad solder connection, or a fine crack in trace somewhere. Eventually a connection fails, this could be due to temperature, but maybe also just random (or both).
This is hard to track down, but I’d apply some mechanical stress to the board if the issue occurs again. (light press on the board, bit of tapping,..)
If you see any change it is certainly a mechanical problem. Hard to track down though.
It’s of course not entirely impossible, that the Juno-66 is faulty, but I can not think of a way such an issue is created. You could try to perform a firmware reset. And if that does not help perform a firmware update.