I had the same issue and was able to fix it by removing the full url (for example: mongodb://myuser:[email protected]/my_database) in the connection tab and only putting in the mongodb server url: mongodb-test.mydomain.com.
Next, in the Authentication tab, I checked the Perform authentication checkbox, specified the Database, user name, password.
I also added the database in the Advanded tab just in case and I can now connect without error.