Same problem.
I’ve had a similar issue, where the left and right channels are unbalanced at low volumes, which can sometimes be fixed after turning up the volume, or turning on and off silent mode. In view of the above reasons, I think it is caused by oxidation of the output relay contacts. So I opened the amplifier cover, opened the black relay housing under the amplifier output terminal, and sanded the relay contacts with sandpaper, which solved the above problem. Hope it helps.