Matt Clear Coat issue - Help

Wow, that's nasty.

Just a guess, but it looks like you just sprayed without shaking the can after the can has been left untouched for a long period, allowing the pigment (in this case the flattening agent) to settle in the can. This results in a big blast of pigment with a minimum amount the associated carrier being deposited on your model.

I rather suspect that if you were to use that can again, even after a thorough shaking, it will deliver a semi-gloss finish now, rather than a flat one.

When using spray cans, shake it till you think you've shaken it too much and then shake it some more. Always.

You can help the paint flow by placing the can in a basin of warm (not hot) water for a few minutes.

The only remedy I can suggest is to strip it all right back and start again.

If Valspar is enamel then get some paint thinner and a soft brush to remove that white gunk. The thinner will not attack the Vallejo acrylic. Do NOT use lacquer thinner!

Like Phil said, sounds like the rattle can wasn’t shaken long enough.