I'm not a playfield clearcoat expert at all, but from what I can tell in those pics, the clearcoat is still hot when the playfield is being assembled. That's the *only* way you'd get those defects. The ink coming up is due to it being bound to the clear. I don't think there is an issue with the ink binding to the wood ... this looks like a clearcoat problem.
I wonder if they're using additives to the clear (like fisheye remover)? (thinking out loud). Doesn't fisheye remover 'soften' the clear thus making cure time longer?
Using plastic washers under the posts should work well for those playfields that are 'mostly' cured. I think you'd have the same problems if washers were used at the factory. While you shouldn't have to do this for a $10K+ machine, you should install washers under the posts the minute you take delivery. Also, don't torque those posts down really tight ... a little bit more than hand tight should be all you need to use.
One final note ... if these playfields are being printed in China, I expect a LOT of bootleg playfields to become available soon ... once they see what they sell for, you'll more than likely see them flood the market with knockoffs.
Using Chinese manufacturing to have playfields cut and inserts assembled shouldn't be a problem, but these companies are stupid if they're giving them all of the artwork to print them.