This is likely to be the cause of the problem - either way, you'll need to put it right. The slipper is slipping too much (lack of drive) and friction welding to the spur (drive suddenly regained). Before long, you'll have no slipper material left at all and no drive at all. Your spur is most likely missing the 'maltese cross', or at the very least it will be partially missing or damaged. The spur may otherwise look fine, the teeth may be perfect - but it's highly likely that it's had it.

So you'll need:

new slipper pads #72131 (you get 2 in a pack), a new spur (47t,49t or 52t) and while you're at it you may as well change the spring/hex-hole washer #87042, nut Z684 (M4 Lock nut), slipper pin Z260 and the slipper plate #72130.

The slipper pads are self-adhesive and need to be alligned with the 'maltese cross' shape and adhered onto the new spur. Follow the diagram in the manual to the letter.

I've found that since I rebuilt mine, I need to tighten the spring right up tight. Before I used to back it off 1/4 of a turn, but now - even with a new sping and lock nut - I have to keep it really tight, otherwise it can (and will) slip. So take JFC's advice and tighten it up - keep things simple.

You still need to check how smooth everything rotates, including the driveshafts/UJ's etc to ensure that your damaged slipper wasn't the result of some other drive-line related issue.

Keep us posted.