I've never had this problem running multiple sites on multiple servers running different versions of php and osticket over the years. So I can only surmise that this is something unique to your configuration and or server setup.
The 1.11 FAQ specifically says PHP 5.6+ and you are running an Older version. I would upgrade to 5.6 (or 7.0 or 7.1) and I would check your slow query log for mysql and see if it sheds any light on the issue.