Annoying clunk when sliding drivers seat back

Our previous Octy used to have an annoying fault where, on sliding the drivers seat back, the seat seems to lock into place and then, usually a few minutes later, it kind of 'clunks' into position and the seat moves slightly as it does. It seems ike the ratchet isn't engaged and then engages suddenly with a clunk.

Found that the brand new Octy does exactly the same thing. It always catches me unawares and is very annoying.

Since the wife always pulls the seat forward, I'm always moving it back so it happens a lot.

Anyone else experience this? I've never had it happen on the passenger side.