Sounds like you need to check everything.
I used to get intermittant off-center, turned out to be the old corroded, and slightly smaller rca jacks on my vintage McIntosh tuner/preamp. Move any cable of any piece of equipment, a contact on the tuner/preamp might get disturbed, one channel making a better contact than the other.
Audio Classics replaced all the rca jacks with new tight gold plated ones, problem gone.
And I now use cables with locking rca jacks, mess about with anything, they stay firmly connected.
There are occasional tracks recorded with off-center imaging. The more revealing/imaging your system, the more you become aware of this.
For that reason, I am a big fan of Balance Controls, especially remote balance.