I have a fresh install of 10.18.1 and it doesn't have the Dropdown container widget. Perhaps it's outdated, or it's deprecated in 10.18? Try updating or replacing it
We probably need some more context information:
- Are you working in Structure mode or Design mode?
- What widgets are on the page?
- Are the widgets you are deleting inside a listview, gallery, or other type of data view?
- Do you have a domain model with inheritance that you are using here?
- Are you using custom widgets?