Can not display Proxmox console due to Connection time out

When I try to open console in proxmox ve nothing happens and I see this error in logs:

no connection : Connection timed out
TASK ERROR: command '/bin/nc -l -p 5900 -w 10 -c '/usr/sbin/qm vncproxy 100 2>/dev/null'' failed: exit code 1

How can I fix this please?

This is caused by the netcat command timing out due to there being no VNC connection in 10 seconds. In my case, this is because Java was slow to start up.

You can log into SSH on the box and manually run the netcat command with a longer timeout, e.g.

/bin/nc -l -p 5900 -w 100 -c '/usr/sbin/qm vncproxy 1301 2>/dev/null'

I've not yet found a way to change this timeout value globally.