Let me start by saying I have used this same setup literally for years now and have not seen this new issue until yesterday.

I have a dual monitor setup. One of the monitors is controlled by a KVM switch; the machines that have only a single graphics port use this monitor via the KVM switch. The other monitor has two HDMI ports that are connected to two computers directly, bypassing the KVM switch; I just switch the second monitor manually between the two as needed. 

What used to happen when I switched to a different computer is that I can use the new computer using the first monitor, the mouse and the keyboard, just as usual. The second monitor, unaffected by the KVM switch, will continue to show the image it is getting from the dual-monitor system. I am used to this; sometimes I even use it to my advantage when the monitor is showing a web page or something that I can still see while working on a different computer.

But, what is now happening (since yesterday) is that when I switch to a second computer, the non-KVM-switched monitor now flashes off and on every few seconds (and just keeps doing this seemingly forever; I did leave it this way for more than 15 minutes last night) . This is INCREDIBLY annoying and makes it impossible to make any use of the image displayed there. 

Another oddity is that this is NOT happening with the other dual-monitor machine. That system is a Dell laptop in a dock. The system with the issue is a fairly new desktop (which did not exhibit the issue for the first few days of use, it suddenly started yesterday). Both systems are running Fedora 32 (but of course they have very different hardware).

I normally use GNOME on Xorg, but I have tried plain GNOME (Wayland) and Cinnamon too and the problem exists there as well. I briefly tried Plasma, but that results in a solid green screen, and when I switch back to the two-monitor system, the first monitor is solid green too and none of the keys respond, so I had to use a remote ssh shutdown to recover.

Has anyone ever seen anything like this and know what I could do to stop it?

Thanks,
--Greg