I was building architecture by having live edit open and dragging architecture from the content browser in UEFN to the viewport. At some point, the entire structure just disappeared. This is because there is no structural support on the pieces, and Creative tells UEFN to delete them.
There needs to be a toggle button on UEFN to toggle gravity because right now all pieces have gravity on by default and when you launch Creative it will delete everything that is not touching a structural point.
In Creative, placing a piece with gravity on an area that has no structural support denies placement, but not in UEFN.
The entire structure that I was building was deleted and lost progress:
Also relates to this ticket: https://forums.unrealengine.com/t/level-design-confusion-after-gravity-destroyed-prefab/594842