Virtual Machines in Streamed Catalog suddenly become inaccessible with the status of the Power State as On (Action Pending), as displayed in the following screen shot:
XenDesktop was unable to broker new connections and existing users were unable to reconnect.
Virtual Machines show “Yellow State” in VCenter, as displayed in the following screen shot:
In this case, unresponsive XenServer failed to restart and was ejected from the pool. New pool master was selected and another slave server had the Volume Group details.
After that, all the 500 Virtual Machines started as expected with correct power state and XenDesktop started brokering the connections successfully.