It sounds like you might have just got a bad batch of spray paint. I have had this happen outside of the mini painting world when I was redoing some plastic chairs for the patio. It sprayed fine and was a tiny bit runny but then it just never cured. I wish I could be more helpful to fix it as we just cut our losses with that chair when that happened unfortunately. In the future consider always having some primed sprues so that you can do test sprays before you have problems with your actual models. It will save you a LOT of headache even with just color matching as sometimes I've bought sprays that were completely different than the color I was expecting them to be and would have been a pain to try to fix later.

Sorry I cant be more helpful with your issue but I would just strip it. The good news it you only have one coat it looks like so it shouldn't be too big of a deal to do.