I just compared the footage from various points in time. The flap positions for T+00:48:12 (pre-entry) and T+01:05:41 are almost the same, then it rotates about its rotation axis until T+01:05:44, but suddenly it starts to rotate about ANOTHER axis, and at T+01:05:47, its at a completely new angle. I think T+01:05:44 is the point where the flap finally breaks (after touchdown, but before splashdown).

I think we have seen motion as fast as the one at T+01:04:22, but the subsequent bounce is surprisingly strong. I still think that the flap was still under some control at that point.

I heard rumors on reddit that SpaceX deliberately removed a single tile on this flap for testing purposes, but I could not find any reliable confirmation for this. They deliberately removed tiles on the engine skirt, though.