2nd layer of landscape mesh?!?!

Hey everyone!

So recently I’m working on a conversion, but I’ve mostly spent time with models, their textures and collision, etc.

Yesterday I tried to flatten and smooth the ground for one of my buildings, but when I clicked ‘Play from here’, I got stuck between 2 landscapes, or 2 layers of if. The top layer is the older, ‘original’ landscape without the flattening, and the lower landscape is the “new” flattened one. [images below]. Does anyone know why this is happening? I definitely** did not create** a second landscape, my Scene Outliner shows just one as well. In the Editor it’s also OK, no double-mesh. I tried to ‘Build Geometry’ and ‘Build Paths’, neither of them helped. I went back to an older version of the map, which contains only my textured landscape, and now even that one has this bug (!!).

I can’t undo it, and can’t make it disappear. Anyone knows a solution for this?

Thanks in advance.