OK, I will try and spray a fresh piece and see if it happens again. I'll also sand down the doors and start laying down a few thin coats.
I'm using an HVLP turbine so ambient air humidity is all the moisture coming through the hose. I spray in my currently unfinished basement that runs a dehumidifier so it should be OK.
As for sources of the contamination I have to do some testing. I will see if it's the sandpaper, the wood itself, the gun, my shop vac attachment I use to clean off dust between coats or the lacquer itself.
I have to find the source. I could just get through it for this job but I would be risking every project after this if I don't.