I ran into clouding SO often, basically everytime I tried a satin or matte varnish.
I have a hard time nailing down the issue.. if I'm applying it too thickly, didn't thin enough, too far away etc... and I had that with purity seal as well as with Vallejo.
Luckily I mostly use models where a gloss coat looks nice because they're either black or mostly metallic.
That said, always remember that if the varnish clouds your mini, you can always apply gloss over it to fix it and try again. Well, at least once
Many seem to swear on Testors though.