I am having an issue with saving flexible content layouts. Every time I save all the fields I have added to the layout get removed from the flexible content layout and added to the top level field groups. If I duplicate a previously made flexible content layout, as soon as I save all fields are removed from the layout.
I can duplicate or create any other type of field.
I am using v 5.61 with wp 5.1.1.
After upgrading to the latest version, my problem was resolved.