Hi Dan.
Please try to use the method I have described with a file from a subfolder in your iCloud Drive. - I’ll bet you crash Rhino every time. 
Another problem is shown in the videofile when saving and the floating toolbar is in front of the dialogue-box(!)
I was unable to reproduce this on my machine. Is anyone else here able to reproduce this issue?
This is a duplicate topic to: Rhino crashes when opening a 3dm-file which as been (intentionally) overwritten by Rhino 5.4 with a new content …let’s move this discussion over there.