When ever you make a map and add meshes to your game, don't add the bunch of meshes at once, and better try to add them each time you run the game, so you can find out the reason of the crashing.
Most of the crashing are because of .particle files, because FH crashes when they are duplicated (and they get duplicated themselves at exporting your map and make your game crash at the next run)
Also you game can crash if the meshes are in a upper version than the one supported by your game, so try to get the meshes "for feralheart" or from feral heart site.
I don't remember other reasons now, but try to add them little by llittle.