A view I created in the database was not appearing in the designer (after choosing "Update model from database..." and adding a check next to the name of the view). I saw no error message until I switched the EDMX to xml view:
In the edmx xml I found:
"Errors Found During Generation: warning 6013: The table/view '(view name)' does not have a primary key defined and no valid primary key could be inferred. This table/view has been excluded. To use the entity, you will need to review your schema, add the correct keys, and uncomment it."
I modified the view to have a primary key. Then I opened the edmx designer and ran "Update model from database..." and the view then appeared in the designer as expected with no errors.