Level extent affected by fbx import containing many buildings

Hi, hope someone will be able to advise me on this. I have many levels in my open world, and I have been importing buildings, many buildings in large batches. Some of these buildings clusters go beyond the normal extent of the level and go into the adjacent level, which is fine because that is where they belong. However, it really messes up the extent of the initial levels. I clearly wrongly thought the buildings would be associated with whichever level/map they reside over in the open world. Anyone know how I can associate meshes to their proper levels/maps?

My guess is that selecting the meshes -> right click -> Level ->actor level -> make current level would be the only and correct approach. At my current stage of development I’m working with over 32K cubes arranged in specific places. Would be nice to know I’m on the right track before digging myself in an even deeper hole.

Ctrl+Alt+(LeftClick drag select) to highlight multiple objects at once then Ctrl+M to make current level seems to be the best option thus far, though the drag select doesn’t seem to want to select everything in the region made. The workaround for this seems to be turn off visibility for the level you are on so that when you move objects to the level successfully, they will disappear. Very strange though that the mouse drag select doesn’t select everything within the selection square.

After 6 hours, 3 lost due to a UE4 crash, and having to restore a backup due to over 10K levels deciding to drift off the maps,I’m now half way there, and somehow left with levels surrounded by white in the world composition editor with a strange smudge above my group of levels. May have a restore again and start from scratch. Some very strange behavior coming from the editor.