Well there you go, your answer has been posted by others, uncured film and trapped solvents, you have both. That SS enamel can stay wet a long time, especially if applied heavy (read that a lot of overlap, slow gun movement, etc.) or too many coats too fast, too slow reducer, not hot enough surface temp, any or all of these things combined make for slower flashing and curing.
Now, under perfect conditions as I remember the window to apply clear over SS enamel is a much longer after the color is applied than say a regular Basecoat clearcoat. That is what I remember, but anyway you look at it applying clear over SS isn't the norm for a reason, it's a bit more temperamental.
Did you follow the tech sheet for recoat time and coats applied?
How many coats did you apply and how long did you wait before clear?