So we will call them "dimples" - just for the sake of describing the problem.

I can confirm 100% it is not the timber. The dimples are on the inserts. The inserts are not made of wood. The problem is definitely - 100% - The clearcoat. This playfield was like glass when we unboxed it. no blemishes except the area under the bicycle girl ramp.

I have never seen this issue on other playfields. I did a quick scan of over 30 DMDs today, and not one of them has this issue. I have seen enough playfields - I've even seen a Dr Who with the clear worn away to reveal the serial number etched into the playfield. The ONLY place I've seen this ;

1 - This game
2 - A game cleared by a backyarder that was too thick and was populated a week after the clear. Not cured.

The dimpling is caused by the ball - that's clear enough. The ball is impacting on a soft clear. In theory, it should be cured by now - yet it is impossible to say if further play will damage it even further. So until I clear this up (no pun intended), it is an expensive ornament..