I created the terrain and saved the project. After restarting, I went into the project, but the terrain disappeared. I turned on the landsqape checkbox but it’s not there anywhere.
the player falls into the abyss after the start
Has anyone encountered a similar problem?
So how do you get the landscape back in place?

Did you save the level/map? Did you openthe same level/map?

yes, yes

Doesn’t look like the landscape was saved. Did you delete the ThirdPerson map taht came with this?
The info on the landscape looks wrong (very small or non-existent)

Try creating a new level (with the floor). Saving it and then check to make sure that was saved.
Make sure to do a Save All after changes.

And what is so to recreate each? I then saved everything and my player ran across the landscape. If I do the mountains all day and then go back the next day, will I do everything again?

Just make sure to do a save all. And check the content folder to check the updated time to make sure it was.

Not sure if you hit a bug or other issue.