Designers: what breaks most often when your file goes to print?

I’ve been a packaging designer in Vietnam for years, and the print-shop handoff is still the part I dread most.

My top 3:

1. Colors shift because the file wasn’t really CMYK

2. Foil / UV layers get mixed into the color file

3. The box looks fine flat, but the artwork lands on the wrong panel once it’s folded

What’s yours? And how do you check before sending: physical sample, 3D mockup, or just hope? 😅