The mount will stop tracking when losing communications with the ExploreStars application either through a dropped WiFi connection, or when the ExploreStars program is shutdown.
You can see the active communications status of the controller by noting the flashing amber LED on the PMC-Eight (G11, EXOS2). That LED shows you the active communications traffic going between the host computer and the controller. Check out our knowledge base article on the PMC-Eight LED's. This communications halt is a safety feature we implemented in case people walked away from the mount with their tablet and the connection dropped.
We offer an alternative version of the firmware that disables this “communications watchdog timeout” feature so that if you disconnect the ExploreStars application from the mount, the mount will continue to track at the nominal Sidereal tracking rate for that mount. You can find that firmware