I just had this problem pop up for me again, 6th or 7th time this year. (No sounds out of main+cue except metronome still works). Caught on video!
This time (as it has been for a few other times for me), the solution was to unplug all cables (except for power and main outs) and drop the octatrack about 1" off of the table. As soon as the octatrack hit the table, the sound clicked back on. Unfortunately, did not catch that on video.
In other news, I just stopped by the Elektron US service location and they exchanged my OT with a new one just like that! Also notably they told me I had an older mk2 model manufactured in late 2017 (not sure if that matters), but I’m hoping I have better luck with this one which was manufactured more recently in 2018. I was also having the screen burn in issue. He also told me they are going to release an update with a screensaver, so that’s great for future screens! Elektron service was AWESOME in person and totally exceeded all of my expectations, I feel like they really took care of me no questions asked. The response I got from the online support folks had lead me to believe I would be stuck with a bad unit if the guy in repair could not reproduce it (which would be unlikely given the intermittent nature of these issues we are having).
Also of note, the gentleman in repairs told me that the metronome is a separate circuit from the mains/cues/internal sound engine. If he finds out what the problem is, hopefully I can find out what it was and post about it here. I have a feeling all of these issues are caused by a loose internal connection or two. I also think it might have something to do with overloading the internal pre-amps, or maybe an internal ground loop somewhere. He is going to look into it! Will keep y’all updated