Okay, this is strange. I did some more testing and in my case it was a particular blueprint that would case the RAM to balloon as long as it was open in the blueprint editor. I tried to replicate a particular circular reference involving an animation blueprint and a pawn blueprint in an empty project, but it didn’t cause the problem.
Back to my own project, I noticed I had a large amount of tabs opened in the blueprint editor which came along from the migration from 4.5.1 to 4.9.1 for that particular blueprint. I closed all of them but the viewport and the RAM usage stopped increasing. I even opened some of my graphs and it’s still stable. I’m not sure if it was the amount of opened tabs or if there is a particular function graph that triggers it (this BP has a lot of functions), but I’ll keep an eye on it and report if I find anything else.
For those who migrated their projects, try closing all blueprint editor tabs and open fresh ones.