If you are using a hypervisor to test Proxmox (eg. Vbox) then changing the video card/display adapter can fix it.
For example VboxSVGA causes the issue but switching to VMSVGA fixes it.
For example VboxSVGA causes the issue but switching to VMSVGA fixes it.
........
Just use apt-cache policy to find the repo of a package:
apt-cache policy lxd
lxd:
Installed: 3.0.3-0ubuntu1~18.04.2
Candidate: 3.0.3-0ubuntu1~18.04.2
Version table:
*** 3.0.3-0ubuntu1~18.04.2 500
500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
&nb........
Failed to open a session for the virtual machine XP.
AMD-V is being used by another hypervisor. (VERR_SVM_IN_USE).
VirtualBox can't enable the AMD-V extension. Please disable the KVM kernel extension, recompile your kernel and reboot (VERR_SVM_IN_USE)
Solution - Unload KVM module (you can't use two hardware virtualization suites at once)
sudo rmmod kvm_amd kvm........