Nvidia driver fails in appvm (4.3 only)

I have migrated my 4.2 template (T1) to 4.3 (T2), and by experimentation, found that no GUI windows of the appVMs based on the 4.3 template (T2). But after uninstalling nvidia, the GUI windows can be displayed.

By GUI windows, I mean the terminal, etc, opened by any standard application in the AppVM that opens a window.

This happens in any VM that was based on the template, regardless of the GPU card attached as a PCI device or not.

Which distro?

debian-13-xfce. I had installed the nvidia package from the nonfree package group as defined in the apt sources list. The driver was v550.