When someone logs off from the XenApp session, Studio marks the "Session State" as "Disconnected" and the "Application State" is "Application not running". If under "Client Address" there is a valid IP Address, all is well, but sometimes there is an IP Address 127.0.0.1 (loopback). In this case the user cannot connect anymore to any Workers of the Machine Catalog / Delivery Group. Most case it is possible to logoff this session, but sometimes I have to logon to the Worker via RDP and logoff the session via the taskmanager > users.

Upgrade to 7.15. 

Problem Cause

Session doesn't log off properly.