lets try a simple minded approach(i'm good at that)lock the wing srvos by turning your equipment on and support your plane on the bench with cans or blocks under the ailerons and see if one has more flex than the other.If the left one flexes up more than the right one it would create less lift on the left wing and make it roll out.I know it works inverted but it may only want to flex one way.I know this sounds simplistic but you have tried everthing else.