I have the exact same issue when resuming from hybrid-sleep: X server process takes 100% CPU and can’t be killed even with SIGKILL. Restarting the display manager from an ssh session works after a long timeout for the systemd unit. I didn’t get anything fishy in the kernel log, though. The only error I have is in the Xorg.0.log, which says
(EE) NVIDIA(GPU-0): Failed to query object info.
systemd suspend and systemd hibernate work just fine.
My spec:
Arch Linux with 5.11.6 kernel
GPU 1650Ti with driver 460.56