Virtual Machines in Aria Operations 8.17.x and 8.18.0 do not show the Oversized and Undersized metrics.
VMware Aria Operations 8.17.x
VMware Aria Operations 8.18.0
This is a known issue in 8.17.x and 8.18. If the VM needs no rightsizing (according to calculations), then the rightsizing metrics will not be published at that time.
There is no resolution at the time. A Hot Fix for 8.18 will be released so sizing metrics will always display a value.