Hmm, well you should be able to do that. The only thing I can think of is do you have a data type named the same thing (Review Relationships) that you might’ve accidentally set the review-relationship field type to instead of the Option Set?
Also, a quick tip regarding naming conventions:
Sometimes it helps to name the field the same as the data type, and capitalise fields that use datatypes rather than text/number etc. So for your Review I might have
anonymous
Service Provider
rating
review
Review Relationship
as it helps visualise which data are datatypes/option sets and which are not
And you don’t have two dropdowns named the same thing? It looks like a bug but there might be something your screenshots don’t show. Have you tried deleting the dropdown and recreating it…