Depends on your field. If sciences, make sure all the preferences are checked (see image). Usually Pubmed isn’t selected as a default setting, because if you select hundreds or thousands of records to run at once, Pubmed can interpret the queries as a denial of service attack and block your isp. Also I know that some functionality is compromised with respect to CrossRef querying and think that might also be a problem, which I understand from other threads, is under investigation.
