I've used Multiplicity for many years and it's worked great for the most part. My primary is a desktop and my secondary is a laptop. Both are running Windows 10. The laptop is connected to an external monitor.
The two computers are connected via Ethernet cables through a NetgearNighthawk AC1900 Dual Band Wi-Fi Gigabit Router (R7000). I've used the same router for about 4 years. The desktop and laptop are about 1 year old. My previous desktop and laptop were Windows 7, and Multiplicity worked perfectly. I do not use a VPN.
Ever since I bought the new desktop and laptop about a year ago, my laptop regularly gets disconnected from my desktop. Sometimes the problem fixes itself after a while. Usually, though, I have to reboot the desktop. (Rebooting the laptop never fixes the problem.)
Sometimes, the problem is even worse. I suspect this happens when my mouse pointer is on the laptop when the disconnection occurs, but I'm not sure of that. When this happens, I have no access to the desktop at all. I can access the laptop, but the mouse pointer is gone. I can only use the keyboard. To fix the problem, I have to shut down the laptop, which lets me regain control of the desktop.
I've put up with this for a year, but I've finally gotten frustrated enough to write. I believe I have the latest versions of Multiplicity on both the desktop and the laptop (version 3.55). The problem has persisted over more than one version. I have updated versions at least once, maybe twice, as new versions come out, but it doesn't help.
I have, of course, tried rebooting everything, including the router, many times. I've also tried deleting the secondary and reinstalling it, and I've tried uninstalling the software from both computers and reinstalling it. Nothing works. I have to reboot my desktop at least a couple of times a day because of this problem.