Juttery (non-smooth) playback of multicam

Very peculiar.

I have interviews where two cameras are combined into a multicamera clip which, in the source monitor, plays back fine. but in the program monitor one of the cameras is not smooth playback. All the other non-multicam, including camera B plays back very smoothly. But Camera a, only when edited in as part of a multi-cam clip, plays back stuttering. (Audio is fine). If I replace each clip with the direct source, it's fine. Annoyingly tedious but fine.

Hmmm...