Moving certain sub groups out of a group cause some of them to appear through a new datasmith import (in a new blank project), but most objects are still missing even with very small groups, and even individual objects (not grouped in any way, directly "at the root" of the scene).
In a specific case (but not in this specific scene), in order to have all objects imported to Unreal, the only way that worked was to "Make Editable" all objects and "Unparent" everything in order to have no hierarchy at all.
This was reported and tested in 4.23 (4.23E0).
Results: A complete hierarchy branch is missing (the group named "MarketHall(2019-08-29)" and all sub groups)
Refer to the screen capture attached named: 2019-09-17_DatasmithImport.PNG
Expected: All geometry visible in the Cinema 4D file should be imported in Unreal.
Refer to the screen capture attached named: 2019-09-17_C4D_Scene.PNG
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-80690 in the post.