Kinda of curious if any one else has used a Radeon Card. One I got is an AMD Radeon Pro WX91000. Haven't received it yet, have always had Quadro, but since I went with AMD Processer, figured I need to stay with more compatible components.
Windows 10 is terrible with how it handles the second monitor. I have multiple bug reports in with them regarding how applications are treated on the second screen. As far as your case, I use docked windows and have never had an issue stretching PC-DMIS between two screens. I've never seen your issue, and it could be any host of hardware/software possibilities.
I'm leaning towards software, Everything is new, new. AMD 9, ASUS x570-E Board, 2 Ballistic 32 GB Sticks. Most recent Copy of Windows, Before I put This Radeon Card in, Had Quadro m4000, Quadro P620, This issue has done the same on all 3 cards. I have no problem with the Docking view, once it is stretched across the 2 screens, in fact my saved view is in Docking Mode. So When Dmis is open, (-minus opening an actual program) it's fine whether on one screen or 2, but if I have to open a program, That's when it MUST be on 1 screen only and it can absolutley not even be a smidge on the other screen or it will lock up, once it opens, I have to right click in Editor, Uncheck Docking View, stretch it across both screens, then I can click on my saved Layout, which Is in Docking View, and everything is hunky dory.
Oh and just to add, no other programs are having any issues, SolidWorks, MasterCam, and other programs I have on this computer, Just DMIS, Even before adding these programs, was doing the same as I stated. I have removed them, for It is not needed on my PC, but it can definitely handle it.