The tanks I have finished so far...not sure what the issue is with the spider webbing. Some areas to have a big issue, other areas are not bothered.

Are you painting over the primer entirely, or just adding highlights/washes and using the primer as your base color? It may be that the Minwax is reacting with the primer. (And is it Minwax polyurethane, or Minwax lacquer?)

Miniwax poly, I have used it both ways on the other dust minis. With the tanks I just coated over the primer with minwax, dry brushed, then a few days later tried to apply the clear coat. It really seems to be with large flat areas. I am not 100% sure if I shook the can enough, my next attempt I will shake it for a few minutes and see.

Also make sure its not too humid when you spray and try krylon matte if the minwax keeps failing.