Why won't my landscapes save?

Hey guys

I have a problem with saving my project when I’ve edited the map

After editing adding trees and making the landscape exactly as I would like, I save it (obviously).

But when I left unreal and re opened my save everything is there- except for the terrain!

It’s so frustrating is there a way I can either get my landscape back or stop this from happening in the future?

Has anyone else experienced this issue?