Client(s) are trying to login to APPX and hang after entering their login information. (APPX may eventually come back and say, Cannot connect to host.)

Having the user logout, and try to log back in again, to make sure that the situation is not due to exceeding your licensed user count, results in that user not being able to log in. Also, if you bring up an NT task list, and do not see WinAppxD.exe in the list, that is an indication that it has already stopped (either you stopped it, or it ran into an error condition and ended itself), and needs to be restarted.

Once again, restarting WinAppxD without a reboot is not guaranteed to work, due to NT TCP/IP implementation. The existence of "Stop" and "Start" buttons in the Services Control panel applet does not mean that these functions work 100% of the time.