Originally posted by TwoUptons 
I’m not sure if this fully fits your description, but the rewind knob will sometimes move irregularly as a normal consequence of changing tension in the film spool.
As you advance the film, the tightly wound film in the canister may unwind a bit more internally. It won’t move outside of the spool, but it may move the knob and mean the rewind knob doesn’t move the next time you wind the film.
If you really want to see if that’s the case, add a little tension on the knob with your fingers each time you wind the film and keep an eye open for movement between shots.
-Eric
This is likely the issue. Also keep in mind that sometimes film may be wound tightly (especially with older or expired film), which can make advancing the film change tension at times.
When a fresh roll is put into the camera, the rewind lever may spin partially, then stop for a couple of frames before starting again as Eric pointed out. Shoot the entire roll and see what you get, then you’ll know what is and isn’t working.
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