Sounds like this issue is occurring only on Mirco produced playfields which JJP uses exclusively and Stern uses for some of their playfields. That may be why the issue isn't occurring as often on Stern games since they use other playfield manufacturers.
In regards to timing for when the issue began my best best guess is late summer 2018 when Pirates started to ship. Dialed In's produced prior to Pirates used Mirco playfields but didn't have clear pooling around posts or post chipping. Something changed with Mirco playfields during the summer of 2018 and from what I can tell they are still being made the same way.
Overall this issue is unacceptable and the last thing owners of a NIB pin should have to worry about while paying record high prices is playfield quality. Want to charge top dollar for these games? Ok but then offer top quality.