Can you try to do a host vmotion and see if it gets resolved? If not, can you shut down the VM's and start them again? I have seen this issue before and a shutdown and start resolved it.
Look at the Alarms tab for the datacenter or cluster - somewhere higher up than the VMs, if the VM Alarms tab is not showing anything. Also check the datastores individual Alarm tabs.
Can you try to do a host vmotion and see if it gets resolved? If not, can you shut down the VM's and start them again? I have seen this issue before and a shutdown and start resolved it.
