Some additional info would be helpful.
I believe you are saying that this is a new problem on a site that was working... So something has changed. Without additional details, all I can do is guess that it is likely caused by a setting that was recently changed, or, more likely, a plugin that was recently updated. Try disabling all plugins, if the problem is solved, re-enable them one at a time until the problem returns. That last plugin would be the prime suspect.