RE: Uncontrollable 100
It seems a case of insufficient dihedral versus too much rudder.
There is a helicoidal airstream from the propeller, which hits the right wing from above and the left wing from below.
Because the roll stability is marginal, it may be disturbed by that airstream.
I would suggest trying to increase the dihedral or adding ailerons (regular or independent spoilers), in order to increase the roll stability or control.
It will good to verify wing wraps and symmetry and lateral balance, as well as taping the hinges' lines.