Repro is easy. Just press generate.
Sorry, can’t say that reproducing this bug is as simple as pressing generate.
Provide your system specs, try to reinstall Studio, and check if you might have any plugins that are interfering with Terrain generation.
You’re leaving out a lot of details here. You should read this post and edit the thread to include the necessary information. Based on what you’ve posted, the engineers aren’t going to be able to do anything.
I looked into the code, and it may be due to the fact that Terrain is nil when loading a baseplate (which is a serious problem). I was able to reproduce it, and the code just starts with defining terrain as the property game.Workspace.Terrain.
A fix is in the pipeline already. It seems to indeed be a race condition where a variable (‘terrain’) initializes as nil in a File>New place.