You are 100% correct sir. The plastic and wood expand and contract at 2 different rates with changes in temperature and humidity. You CAN NOT prevent this from happening ever unless playfields start getting made and formed from 100% plastic. Even home use machines will experience this unless the game is never turned on and it is stored in a climate controlled room and never moved .... even then I would bet it will still happen to some extent. The Clearcoat is just too thin and brittle to handle the changes and it cracks and starts to lift off the surface with the least adhesion. (also a note here paint in general does not like to stick to plastic without the use of special products and procedures, and I doubt that any Manufacturer goes to that extent) Is your insert shrinking? Probably not, not this soon anyway, but it is moving enough in relation to the wood that the clearcoat can't handle it. Possible reason is either cheap clearcoat or very thin in the area.
Not talking about games of old as the process and materials used back then are different than today, so lets focus on modern (new) pins.
What can you do as a owner to minimize this effect from happening? Unfortunately not much, unless you are willing to strip down your brand new machine and have the PF clearcoated with a HIGH END clearcoat that has Self healing and has flexing capabilities (yes there is actual real products like this used in body shops today). So you might think again about that investment in the LE models if you plan to keep them for more than your normal time frame. Stern does go through a extra process for the LE versions ... sometimes it is extra clear and sometimes the product used for clear coat is a better quality (example; Diamond Plate), both translates into more expense on their side which is passed onto the customer.
How to repair this before it gets worse .... first find out if your vendor is willing to do anything.... doesn't hurt to ask. ---So the best thing to do is strip it down and have it cleared again. If that is not feasible then you can use ... this is not for the faint of heart ... your wife's clear enamel fingernail polish. You need to either apply it with a small brush or syringe and you need to get it under the edge that is lifting, you will have excess that you need to wipe off and will clean up in later steps but it is important that you get it under the chipped surface to eliminate any air pockets. Let it dry completely and then you will proceed to LIGHTLY sand smooth with 1200 grit to 1500 grit sandpaper, this is a very delicate process as you can remove too much of the original clear very easy and cause more problems over time. You then Polish it with your choice of compounds, Novus 3 - 2 - 1 will work here.
If this sounds a little too much then you could try to recruit the help of a professional Automotive Painter (hopefully you know someone that could help you out, we normally work well for Beer and BBQ)