Uninstall FeralHeart, the Media/Exports/Presets/My_presets/Screenshots folders will still remain. Copy those folders and paste them in another folder that is not FeralHeart. Then delete the Feralheart folder. Then download and install the game again. After it's done, copy the same folders and paste them into the FeralHeart folder. Let them overwrite. Your custom everything will then not be lost.
Hopefully this will fix it.
Also double check your heightmap is: 513 x 513, .png, one layer, grayscale, no alpha channel. If any of these things are not right, it will make the game crash.