I have some Colours of War primer that I've been using for AT-RTs, but the surface is quite smooth, meaning the first coat or two of other colors tend to slide around. Not a big deal for the RTs as they don't have that much non-base color, but I'd like to use the same base for some troopers and I'm worried it's going to be a mess.

Any suggestions? My first thought it so hit it with some matte sealer to give it some grip. That seems unlikely to do much harm, except for a bit of paint buildup. Any other good ideas?

That’s strange behavior for primer isn’t it?

Your matte coat idea would work but you are at risk of filling in a lot of detail that way. What color is the primer? I assume it’s a rattle can rather than a brush on or airbrush primer.

It's a rattle can. Firefly Green is the color name. And to be fair, it is more of a spray that can be used to prime. I'd say priming and then spraying might give more grip, but could run even more risk of detail loss. I might just end up doing more brushing than I'm excited about.

Yeah, I wouldn’t encourage you to spray it twice with a rattlecan.

I picked up an airbrush and I’ve tried to use a brown primer as the base coat for some of my Rebel troopers, but the problem was I couldn’t color match my mistakes and had to paint over the brown parts anyway.

make sure your rattlecan is for plastics, not all primers work on plastic. Wash your miniatures too. I lighter primer coat is better than a heavy one.