Thanks for the scene. I think in this case it's a simple case of maths. The frame from map feature controls the playback using the greyscale value of the map. This means you could potentially have 255 full frames. In, this case there are 99 frames being sampled which doesn't divide well into 255 (theoretically a new animation sample every [2.5757,2.5757,2.5757] RGB). So I think it sometimes skips or adds samples here and there due to rounding and causes a small stuttering effect.
Changing the animation and the number of samples to 128 might help to smooth it out.
Best,
Paul