I tried uploading an image, but the forum software does not seem to allow that!

I needed to upload that elsewhere :-/

Good catch, I did not even notice. I leave the 6.3 mm cable typically connected to input 3, even when no instrument (guitar/ bass) is connected. But input 3 should not be the cause, because it was not in the mix of the two output channels. To double check I unplugged now the cable and indeed the problem remains. I tested a few things and it seems to be related to the Balance-knob of AN1/2.

Store your workspace. Then use Total Reset and rebuild it, starting with the issue itself (Mic in copy mode to phones and Main Out). If that works then the above state was either corrupted or had hidden settings that changed the routing gains.

I have used 'Total Reset' and just enabled the mic for the two channels and mixed that to one output channel. The problem remains. I do not understand this. I was checking also if some other settings in Windows 11 could be the cause of the problem, but do not see any. I made sure all automatic audio enhancements from Windows are disabled as well. No change.

The system where I see no problem uses Windows 10, in case that matters possibly!?

P.S.: The matrix view shows now the default settings after a total reset, so that should also not be a problem.

System is:
Babyface Pro FS with AKM chip, Hardware revision 203

Problematic system: Driver version 1.245 on Windows 11

System without problems: Driver version 1.219 on Windows 10

I have tested further on the problem system. When I do not copy AN1 to AN2 but just use the mic in AN1 and set the balance to (0) middle everything is fine and both channels show the same level in the output. Why the AN1→2 works without touching the channel balance on the other system is still a mystery to me.