Gustard X30 disappointment

Curious about something -- after the first time it dropped the right channel, how did you get it back? Did it come back on its own? Did you get a replacement unit? Cycle on/off? Adjusted or used different cables?  Something else? The circumstances would influence your decision. 

It had been idle about 4 hours, tried playing with roon, then with coax same no right channel, rebooted same, turned off for a few hours and worked again.

today off all day till afternoon, and no right channel again

Did you check the line-out connection on the right channel and also try a different cable from the DAC to preamp/amp?  If that doesn't fix it, sounds like it may be a loose internal connection. Might be worth opening the case and checking to see if the internal cables are all fully seated. Also, poor solder joints can also work intermittently, though these are rarer these days than in the past when circuits were point-to-point soldered. 

If checking the cables and checking the internal plugs doesn't do it, I'd suggest you just ask for a replacement. That assumes you like the sound when its working.  NO manufacturer has 100% perfection from their production line and you also have the possibility that something could have been rattled in transit.  

I wouldn’t mess with this — Gustard has had a history of having some reliability problems, so I’d just return it and if the second unit has issues I’d punt and buy something else.  You could get the Denafrips Pontus and Hermes DDC for just a little more than the X30 just for one example.  Best of luck.