One other note, I also have a third PC working with multiplicity. When I look into the advanced firewall information, both entries for StarDock multiplicity show the profile as "Public" and the Windows defender firewall is on. The profile of both entries on the remote desktop PC mentioned in my above post shows "Private". Why would that be?

Multiplicity will setup the firewall entries on first install.  The ports are only open for a network that is considered private for security reasons.

Microsoft have a frustrating ability to set a network to be considered public after a new Windows install in which case your firewall would block all the Multiplicity connections as it will be seen to be a non trusted network.  In that case setting the network correctly back to home/office would resolve the issue.

The port fix or what Neil said?  Its for bragging rights   

He is right about the Public vs Private, however. What he mentioned is part of this:
https://forums.stardock.com/486104/multiplicity-support-faq#connectionissues

But its rather long to follow and I took a shot that it was just the ports that were hosed.