The curve at the frame after the cycling keyframe is matched up to frame 2, instead of frame 1 like it should be. The following two images have frame 41 shown with frame 1 and frame 2 previewed, respectively.
The second one matches up, which is frame 2. So the fix for the bug would be to use the value for frame 1 right after the cycling keyframe instead of frame 2.
The effect of this bug can be described as a "catching" look for a looping animation. I think it might also be causing another bug. I explain the effect in more detail here:
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