I play as Unfallen. I did force peace and finally did alliance with Riftborn AI faction. Since I started to vine their systems, I get same message every single turn. It's related to my vine systems dpreading out like a disease. Not sure, if this happens in general with every other faction I start to vine systems, so I can only offer this happening with Riftborn faction, yet. Would be nice, to prevent from with an upcoming patch.