Looks like the flap is mounted and seated in such a way as to have its natural position deformed lower on the right side. As the ball travels across that lower portion it eventually impacts the ramp which is raised on that side relative to where the flap leads the ball. This abrupt transition at speed seems to be the source of the sudden change in direction of the ball.
...though my eyes may be deceiving me, it’s tough to visualize even with these great photos.