This usually happens with forms
When I move the form to a new section or column the parts of the form that should be visible in the layout tree disappear.
im not sure whats going on but one of my forms was massive and took me a couple days to rebuild. I thought I did something wrong but now it happened with a login form too I think maybe there might be an issue?
Refreshing the page / data does not work. when it happens I lose my undo history.