Asset from open world demo crashes engine

Hi,
I have just started developing my game and have this issue with an asset i added from open world demo collection.
everytime i try to open the hilltree asset the engine becomes unresponsive.
When i tried to use it as the static mesh in a foliage type it also crashes. it shows that it is loading and gets stuck at some point usually around 97% or 53%.
ive tried adding the contents to other projects and fresh blank projects but its always the same. infact the hilltree_tall also causes the same problem. other assets such as sm_fieldgrass work fine. I dont know what is causing this. any ideas on how to fix it.
im using engine 4.16
tried deleting derived data cache and saved/intermediate folders from all projects but it still didnt work.
Thanks for your time