This is what it looks like in the profiler, takes around 10-15 seconds and the whole editor is just frozen. It goes away when removing ProBuilder from the package manager or reverting to 2.9.8f3. (which we can't do due to PB 4 having migrated components and other things en masse) We are using Unity 2018.1.6f1. Happens with an empty scene, doesn't matter if anything PB is in the game. I could try to run the profiler in deep profile if needs be, but I'm not sure my computer will be able to handle this... I can try to provide further info, but this is all I got for now.