My guess would be the decals weren't completely dry before flipper buttons and bolts were tightened.

I have mixed feelings about Sterns customer service. Chas was extremely helpful when I encountered a weird problem on my KISS Premium. When my demon disc started making an awful screeching sound Patrick sent a new motor. I was grateful until I saw the motor they sent was the rejected ones with cheap rubber that shits black all over the playfield. I know for a fact the Pre/ LE ones have the upgraded discs which are more playfield friendly. Pat insisted otherwise. I offered to pay for a new motor. I just wanted what my pin came with. Never heard another word. Kinda left a sour taste in my mouth but I'm still very happy with my purchase. Hope the OP finds a solution they're satisfied with.