Engine crashes after importing landscape

Hello, I’m having an issue creating landscapes in my project for some reason. Everytime I import a landscape from a height map file and go back to place mode, it simply crashes… The landscape imports just fine, but as as I leave landscape mode, the engine crashes. This also happens if I save the level after importing.
It’s not the terrain file itself because I have used it elsewhere earlier without implications.

This is what the log is telling me after crash.

[2016.07.05-19.54.50:605][219]LogWindows:Error: === Critical error: ===
Fatal error: [File:D:\Build++UE4+Release-4.12+Compile\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp] [Line: 717]
Rendering thread exception:
Assertion failed: Result == FPropertyAccess::Success [File:D:\Build++UE4+Release-4.12+Compile\Sync\Engine\Source\Editor\LandscapeEditor\Private\LandscapeEditorDetailCustomization_NewLandscape.cpp] [Line: 989]