Airbrushing Tamiya Spray Paints

I've been airbrushing models on and off for about 20 years now and I've been airbrushing decanted Tamiya Sprays for about 2 years. Now all of a sudden I've gone stupid or something.

I'm having major difficulty in getting the Tamiya TS paint to give a proper finish. The latest episode being tonight where the white primer is being a real pain. I can lay down an initial mist coat no problem but as I build up the layers the primer takes on a grainy finish with actual dried paint dust accumulating in little 'balls' in certain areas of the model.
I constantly have to smooth the finish with 1000 grit sandpaper.

I can't even spray a gloss colour right now without this same thing happening in one form or another. The worst areas are when I'm spraying inside a confined space like the inside of an F1 monocoque. The paint is so rough the carbon fibre decals don't stick properly.

I never had this problem before and can't figure out what the hell the problem is. I've tried spraying at different air pressures - 5 psi to 15 psi but still no luck. The only thing I can think of is that the decanted paint has thickened since being decanted into jars.

I'm using an Iwata HP-C and it functions properly. It's only these blasted TS paints that are giving me problems.

What air pressures do you guys use for TS paints and what distance do spray at? Any other suggestions are appreciated.

I feel like such a newbie right now

Btw, I did go back and read the ABC's of Airbrushing article.