Three years back I had five comebacks in two weeks after our shop switched primer brands, and I swore up and down it was my hands getting lazy. Turns out the primer was shrinking different under the new clear and every edge I trusted was lying to me. What changed my mind was keeping a log for a month: booth temp, product batch, hours on the ticket, and what got cut. The pattern showed up fast, and it was the hours cut plus one bad batch of clear, not me. I used to blow off the log idea as a waste of time, but now I won't spray a big job without writing the batch number down. Your painter might be onto something with the flash time, but the cut hours are the thing I'd track first, because rushing is what turns a small product quirk into a comeback.