Have had the same issue with Arcam receiver (or believe it is the receiver).
After it warms up, the soundstage drifts to one side due the loss of volume in one of the speakets. Sometimes even accompanied by a subtle crackling noise.
Once I turn the receiver off and then back on, everything goes back to normal for the rest of the listening session.
Could be static accumulating somewhere but not sure. Definitely not IC, as the problem persists when switching between coax and hdmi.