when I migrate all my assets from 4.18 back to 4.16 (because GearVR does not work in 4.18), they are not loaded/registered/visible in the Editor. The only things visible are the empty folders. The assets are however sitting in their corresponding folders on my HDD, just not recognized by 4.16…
Pretty sure you cannot directly copy any assets from a newer version to an older version; there is no fix for that. The only way that’s open to you as far as I know is by switching the unreal version of the project itself.