Drupal 7 Views 3.13 Filter groups returns nothing if one group is empty
I think this is a bug/changed behavour in views introduced a long time ago.

A workaround might be to select the Reduce duplicates checkbox from one of the fields in OR group filter - which will transform your query to LEFT JOIN instead of INNER JOIN.



I found the solution here:
https://www.drupal.org/node/1766338#comment-6973984

It worked for me in Views 7.x-3.13