Painter: Airbrush suddenly blotchy/ banding/ halo....

In the middle of my latest painting the Digital Airbrush started behaving strange. If a paint a first layer it behaves normal. If I then add a new layer on top and paint there, the result is thick, textured and produces strange blotches and halos. I've been using painter intensively since 2013 and never have this occurred before. Tried all I could think of. All possible resets etc I am using painter 2020 on a MacBook Pro mid 2015(Catalina).

Since I paint for a living I am somewhat time strapped and will be sooooo ever grateful for any help.

Thank You

Senju