800 L &R channels issue

[hardcore]

3 days ago I noticed the right channel is louder than left
First I switched the speakers output and the left speaker was louder.

I wasn’t sure what to do and wanted to avoid Devialet service so I followed some of the recommendations over here
1. Checked balance . It was set to “0”
2. Reset the amps ... didn’t solve
3. Reinstalled the firmware, since I’m using 7.1.3 I upgrade for 10, it didn’t solve the problem
4. Rewrite new (identical to what I had ) setting using the configuration tool, problem solved
5. Listen for a day and downgrades back to 7.1.3
Just sharing

Are the two amplifiers power cables connected to the same power outlet duplex, or as close as possible? Perhaps you can try that?