Looking good in the primer Bill, and sounds like you're having the 'Humbrol Problem' - it's one of the intermittent problems with most Humbrol paints these days, since the demise of Humbrol as a company, and the closure of the factory. Just second-rate products I'm afraid - the reason I need to change after using it for 50 years.
All I can suggest is to stir it at least 100 times (seriously), and decant some, stir it again, and then again immediately before use. You may need to reduce the ratio of thinner too, as this may be causing, or adding to, the separation of the pigment. Even after all this, it will possibly take a couple of days to harden fully, preferably in a warm, but not humid, environment.