Think this is designed to make sure users go crazy.
My primary need for network connections and file sharing between these two computers is to sync files so that I can work seamlessly on either computer...
So, I just ran my file sync software on the Win8.1 computer (which always works when the Win10 computer is turned on) completed the file sync, then climbed two flights of stairs (I'm getting too old for this) to the Win10 computer, clicked on the shortcut for the Win8.1 computer and had an immediate connection.
Perhaps the step that I missed was logging in as admin, then relogging in as the non admin user, but I didn't run a file transfer or file sync before I returned to the Win10 computer. In most cases, rebooting does not prevent subsequent reconnections to the Win8.1 computer from the Win10 computer.
If history holds, I will now be able to connect from the Win10 computer until something such as a windows update runs a reboot. Just updated my "tips" file to include this step next time.
Beverly Howard