Hi Tesla,
when you get no information when monitoring a host, it’s normal that your virtual machines are still working, it seems that OpenNebula can’t get the info from the monitoring probes but it won’t affect the KVM processes so VMs will be running.
Is this problem solved without intervention? I mean does the monitoring info refresh after a few minutes or host allocated memory and CPU info is set to 0 permanently.
If possible when this problem happens, and if you can’t find any info in the /var/log/one/oned.log could you post the output of this command?
onehost show HOSTID -x
where HOSTID should be the ID of the host that you’re having problems, e.g 8 in your screenshot
Also though it may be not related but just to discard browser, you may try to open the Development Tools in your browser (Ctrl + Shift + I) and check if you have any errors in the console tab and disable the add blocker when visiting OpenNebula’s Sunstone.