3 computers in an inverted L formation.  Replace primary and moved from Windows 8.1 to 10 with 3 monitors.  Computer above this is Windows 8.1 with 2 monitors.  These work just fine.  Third computer to the right up upper (or any other position) is Windows 10.  The third computer shows connected but does not take the mouse.  AVG antivirus and firewall all set to accept all Multiplicity.  Multiplicity version 3.44 build 0090 on all computers.

Third computer used to work fine until primary died and was replaced.