In the latest preview in Macos, data module is behaving strangely:
Load two models in a blank scene
Create a NewFolder
Put the models in the NewFolder
Hit the visibility icon at the NewFolder and notice that those two models are now moved out of the NewFolder (they are at the same level, not nested in).
Subsequent ones (newfolders) do not show this behavior. They work correctly. This is vanilla slicer.
I have noticed odd bugs like this in subject hierarchy for a long time (I think since at least 5.6), but I never successfully came up with a reproducible series of actions which triggered incorrect behavior. Thanks for reporting and finding a reproducible way to trigger. Hopefully this will help lead to a solution!