Category/Tag aggregate page only displaying latest posts if an admins

Individual category and tag aggregate pages are displaying the latest posts only for admin users.

For an unauthenticated user, they are only seeing posts from Dec. 2013 or older. I was not admin on this blog until this week, so I don’t know what updates were made around December of last year – if any.

The theme is custom. I am guessing that the archive.php file was either modified improperly or that a plugin is causing an issue.

Any suggestions? All help appreciated. Thanks!