Check what contents does your DB has in the Department Table.
Once done, do a select query on your Department Table and see its contents.
If you dont like some of the contents(which somehow got in), delete them and then preview your page.
Can you also show a picture of your SignUP page, Department Dropdown > which association you have selected? Please attach Screenshot of the Studio Pro.
Could it be that you have another Department Table(Entity) somewhere else which is selected in Studio Pro for the SIgnup Page?
I think you may check the attributes in the entity that are association with another entity.