One more thing to confirm. Check the wing fuel tanks are actually taking the amount of fuel that is supposed to be in them.
I once experienced an aircraft that had a damaged fuel tank (it had imploded due to a blocked fuel vent). The gauge read full and it was, but the capacity was reduced by at least a third. The lateral c of g was quite a long way out and it gave some of the roll symptoms your pilot reported.
It also backfired like hell during PFLs when the throttle was opened again due to partial fuel starvation, and the engine then developed the habit of stopping in a spin but that, along with how the vent got blocked....is another story.
This fault probably won't be picked up when the aircraft is weighed, due to the tanks not being full for that purpose.