Splitter/Scaler issue

[dadopave]

Having a very strange and confusing problem - 2 machines with nearly identical setups, one works, one doesn't. Both used to work and the 1 change since then shouldn't be causing this.

Ok here's the system overview: 2 of my computers are hooked to separate J-Tech Digital Scaler/Multi-Resolution Output (MRO) splitters, model JTECH-18GSP14M. On output goes to the 4k KVM and into a 4k screen, the other goes into an 8x8 HDMI matrix switcher which is hooked to 3 other monitors and a TV. Normally the TV displays my TV and the other monitors act as additional screens for my workstation, but I use the scalers and matrix switcher so I can clone the display from the gaming rig on to any of these. This process worked flawlessly up until a few days ago for both systems. Now it works fine for my workstation but not my gaming rig.

The only change I've made recently was to replace one of the 2k screens with a second 4k screen, this time attached to the matrix switcher(it previously exclusively had 2k screens). The switcher is smart enough to ask for the right signal from the scaler, so the newly added 4k screen displays a 4k picture when set to the scaler input, but is supposed to send a 2k signal when set to a 2k output. Again, this works as-advertised on the workstation. The gaming rig will output a 2k signal when the TV is set to that input, and it will output a 4k signal to the 4k monitor. However, if either of the remaining 2k monitors are set to that input, the TV goes into an out of range mode and no signal is delivered. The 4K screen is unaffected by this.

I am not 100% sure the problem started when I installed the new 4k monitor. I did not think to test it immediately before doing the install, so it could have been going on for a little while before that(though I can't imagine why). I know it was absolutely working flawlessly after install of the matrix switcher, which was a couple of weeks ago now. If I bypass the matrix switcher(that is, run the scaler directly to one of the 2k screens) it displays the downscaled image just fine. So wherever the problem is, it's definitely in the matrix(please insert "glitch in the matrix" joke here). But as with most vexing problems, I cannot figure out why it works fine for 1 computer but not the other.

Both machines are running windows 10 and nVidia graphics cards. The gaming rig has an older GTX 960, while the workstation is using a pair of non-SLId GTX 1070s. The only real difference between the two is the workstation has multiple monitors while the gaming rig just has 1.

I can post full system specs if it sounds like it would be necessary, but at the moment I'm kind of lost. I frankly cannot imagine what to try next, except maybe to put the old monitor back and see what happens.