Well, that was fun while it lasted....
Some people have reported channel imbalance, so I downmixed to mono and tested. Everything good -- dead center image.
But then, in the middle of a song, the right channel suddenly dropped to maybe 30% volume. And that's where it is right now. The problem is not the cable. Switched cables and same issue.
Seems to be a similar build quality story as the original 1060s (I was an early adopter, there, too, with the cracking wood and terrible mmcx connectors).
So, here's the question... replace now, or return for refund and wait until M1060C v2 comes out?