I am really struggling with this issue.
For some reason, the hierarchy below the Named Slot I added to the User Widget is not saved.
If i restart the editor, any previous additions will be lost.
In the screenshot, Overlay_79 is added to the Named Slot called Header, but after rebooting, an error occurs and there is nothing left in the slot.
In rare cases, it may appear if you reload the User Widget that is causing the problem, but it depends on luck.
However, the additions may be preserved in other places of use. I don’t know under what conditions.
Does anyone know anything about this issue?