VM only appears on single screen at 1024x768 resolution

[Tim_Myth]

One of my users has had a Windows 7 VM with dual monitors for years. When she logged in 2 days ago, her VM only appeared as a 1024x768 screen on a single monitor. Both monitors function as expected on her local machine (Windows 10) and do the standard 1920x1080 resolution. But when she logs in, one screen stays black and the other has a postage stamp sized VM. The mouse moves across both monitors. I tried all 3 connection protocols, and each behaves slightly differently:

• VMBlast appears on monitor 2 at 1024x768. If I set it to a Window rather than All Displays, the desktop resizes.
• PCoIP appears full screen on monitor 1 but exhibits random flickering black outs.
• RDP stretches a single display across both monitors.

I uninstalled and reinstalled the latest Horizon client, then I uninstalled and reinstalled an earlier version (4.10). No change. I also logged in to her VM from my work station, and it does the exact same thing. If I log in as me to a different VM, the VM appears normally on both screens. My understanding was that VMs took their display settings from the local machine, but this issue clearly follows the VM. What do I need to change on her VM for this to work properly?

[rogal7]

Any recent changes to Parent machine or any change on the End User workstation?

[Tim_Myth]

On the 9th we upgraded our ESXi hosts to 7. The end user's Surface Go and my laptop are running Windows 10, so there were patches on patch Tuesday. We're both completely updated according to Windows Update, so presumably we're running the same version of Windows.

I did find this thread: https://communities.vmware.com/t5/Horizon-Desktops-and-Apps/Multiple-Monitors/td-p/478653 It sounds exactly the same as my situation, however the Max Monitor settings in my environment are all set to 2 already.

[KenSong]

Can you check VRAM size and see if increasing the size makes a difference

[Tim_Myth · Accepted solution]

Thanks kernsong, but I actually figured this out. Looking at Device Manager, I saw the video driver had reverted to the standard VGA driver. I tried running the VM Toolos installer again, but it would crap out at installing the WDDM driver and roll back changes. I had to manually update the driver from Device Manager using the driver on the VM's C drive (c:\Program Files\Common Files\VMware\Drivers\video_wddm).