Unreal Engine Export deletes Map Ground

Hey, i am currently making my Game in Unreal Engine 4.

I made a Landscape Map for my Envirment and then i wanted to make a tempory develepment Export to show my progress to a Friend.

But in the Export, the Ground of my Map is completly missing (Image 3). Like you can see in Image 1 and 2, the Ground is fully working and visible in the Editor of Unreal Engine.

I am pretty new to Unreal Engine, but i although researched a lot on other plattforms, but i couldnt find a Solution or people with the same Problem.

I would be so thankful if somebody could help me to fix this.