Why does the VM web console hang up even though the VM is not vMotioned or vCenter session has not expired?
Please give us your opinion.
This is the same symptom for most non-specific VMs.
As your post needs moving to the area for vSphere, I have reported it to the volunteer moderators.
Need more information on your environment:
What version of ESXi and vCenter?
Does it happened with all VM's i.e Windows , Linux etc...
Does it only happen at certain times of the day?