Could this be related to this earlier bug?
We are also getting this error in Moodle 3.2. It seems when there is a question with tags and 'Enable tags functionality' setting is enable, it again try to add the tag to the question and throw error. But if tags functionality is disable, course imported successfully without throwing any error.
@Russ Instead of deleting tags from a question, disable tags functionality from 'Advanced features' before import. This worked for me.