nothing interesting in the above log.
try the qm unlock 100 command, if that not helps please provide us with the output of
qm config 100
you could also run journalctl -f before restarting the VM for more details of the Syslog
In general, the noVNC is slower than SPICE  or VNC , however, to narrow down the issue, can you test SPICE/VNC on a VM to see if the issue is a general issue in your cluster?
Do you have a backup for the VM? - if yes, is the last backup works?
May I ask you what is the USB passed through on the Ubuntu VM?
Could you check the Syslog during the start of the Ubuntu VM journalctl -f? and please post the full output of pveversion -v