And it could either be wing twist or a difference in the two aileron servos. One might be stronger in it's movement than the other.

But warp or misalignment is probably more apt to be the reason. Got any aileron trim in the plane to get it to fly level? When you look at the wing remember that the ailerons are part of the wing too. If they've been adjusted a bit to keep the plane flying level, there was something out of alignment that needed the ailerons to correct. Now you got two things fighting each other.

BTW, sometimes the tail causes problems like this. If the elevator halves don't work with the same force they can yaw the plane when they're pitching it. A weak connection between the two elelvator halves can give that kind of problem. You got a servo directly driving one side but a connector driving the other. A connector that's worn some slop in either elevator half can be a problem. Too weak a connector can be a problem from day one. I just finished an ARF that came with a halfway fractured metal connector. You could barely see the crack, but after working it with my hands, it broke. Some ARFs come with their connectors installed. You'll have no clue if their connectors were cracked.

A buddy of mine built a beautiful model of a 40s Texaco model. Those were freeflights with one elevator half ground adjustable. So the plans showed one "working" elevator half. So he made his model with one elevator half. When you give it quick, strong elevator movement, it yaws to match. Up gives a yaw one way. Down gives a yaw the other way. Same action you'll see when your elevators aren't working together with the same strength. And when you yaw a wing that's about to stall, it will usually stall the same wing every time. The advancing wing winds up seeing increased AOA due to the yaw. And AOA is what stalls a wing. Or one side of the wing.