Koyasil has such great food production that my population filled up with Unfallen very quickly. I've discovered several Guardians but there are only two on my planet - the rest are nowhere to be found. I don't see any transport ships with them either. They are just added to your population automatically right? What happens to them when there's nowhere for them to go?

Guardians are added to the planet on which they're discovered. If the planet isn't colonized yet, they'll just wait there until it is. I'm not sure what happens if the planet is already full and none of its population can be displaced onto another planet in the system, but in your case it's more likely that you're looking for them in the wrong place than dealing with capacity issues.

As UE I get a lot of guardians on my planets, maybe it's where yours are going : elsewhere in another empire?

HundredBears wrote:

Guardians are added to the planet on which they're discovered. If the planet isn't colonized yet, they'll just wait there until it is. I'm not sure what happens if the planet is already full and none of its population can be displaced onto another planet in the system, but in your case it's more likely that you're looking for them in the wrong place than dealing with capacity issues.

Thanks, this is what I was missing. I did end up figuring out they stay on the planet they are discovered on, when I was playing a different faction and noticed I had a Guardian. I'm still not sure what happens to them in the case where you discover one on your planet and there are no population slots left (or even in your empire).

Guardians create a permanent extra population spot on any planet they inhabit when they are discovered.   You never have to worry about them taking away a slot.