Ha!
I’ve had this.
It’s a rotation in there somewhere. This happens in sequencer occasionally, when you try to add a rotation keyframe between two existing rotation keyframes. UE will toss in a extra rotation with the new keyframe.
If these are blended animations, again check your rotations (which includes checking any new animations you keyframed yourself, scrubbing keyframe by keyframe at the end).
If this is sequencer, redo your end keyframes, typically the second to last keyframe in the series. Not sure how you’d track this down in the animation blend space.
Either way, I think you have a full rotation in there and simply need to find/correct it.
Happy hunting and welcome to the community.