Sounds like your paint is fine and it might be technique. Could be you are overheating your jigs (before you apply paint) or you might have increased your cure temp/time. New oven or heat source?

Usually high humidity will cause your paint to clump.

wicklundh - there are several mediums that can be used for filter material. For the problematic paint you should use a membrane with a larger pore size, maybe 3 micron...