Let us discuss the possible reasons for getting the CLUB OFF-PLANE on the BACKSWING and DOWNSWING, and the best ways to STAY ON-PLANE. I'll start with a couple, then others chime in.
Off-Plane
1. Right Forearm off-plane at Address. I realize that many(most) do set up with the forearm off-plane, but this is one possibility.
2. Changing the BENT RIGHT WRIST angle. This should not change at all throughout the Stroke, except briefly in the front part, between Follow-Through and Finish, when the arms MIRROR the BACKSTROKE conditions.