It appears from martyj pics that it is not happening on the inserts...so maybe the softer timber is the weakest point?

There are some inserts with dimpling, however, not deep depressions or craters as on timber areas. Another anomaly we found today was serious "orange peel" in the top RH corner where the rollover are located - further proof that this playfield's clear is way too thin.

I spent some time testing the clearcoat theory - "Pinball Mythbusters" ? I took the exact ball out of TWD LE and I dropped it on several playfields in my factory.

To ensure the testing was fair, I placed a flipper bat on four other playfields - all clearcoated - in an area that is not really seen and has no prior wear or damage. I placed TWD LE ball on the top of the bat, and allowed it to drop on the playfields. Here are the results ;

Genie - Ball drop under apron area - Nothing. Perfect - Admittedly - this is a very thick clear. Tried several times. Can't get any reaction.
T2 - Ball drop under apron area - Tiny dimple after 2 -3 ball drops.
Sopranos - Ball drop under apron area - Tiny dimple after 2 -3 ball drops.
Stern Playboy - Ball drop under apron area - Tiny dimple after 2 -3 ball drops.

Drumroll .. .. .. .. .. .. .. ..

TWD LE - Ball drop under RHS flipper - left a massive crater in the clear.

So it would be considered to be normal to have small dimples in a clearcoated playfield = Yes.
Metal ball against clear over timber - over a long period of time.
The issue with TWD LE is simply a case of VERY poor coverage of the clear, and way to thin for a $11,000 pinball machine.

I'm hoping that the problem is isolated to this one playfield. I will be contacting Stern for a replacement playfield. Thanks to the guys that have popped into have a look at the issue.