Hi krozig87,
I could not reproduce your issue. The computer on right and PC1587 are the same PC, however each need to have their own unique HotKey. When I used each, as expected, they went to the correct PC (the left margin of the left-most monitor).

If you believe you've set it up correctly and it just isn't working, try deleting them all and recreating them with different HotKeys- ones you are certain are not being used by Windows itself or other applications.
If all else fails, follow this guide purge/reboot/reinstall/reboot and see if the issue persists:
https://support.stardock.com/space/SHC/1347158073/Multiplicity+purging+and+re-installing
Adam McGuinness
Stardock Customer Support Specialist