Get-stat -Entity $rp - Does'nt return any data

Good morning,

I'm trying to get performance data from ressource pool object but Get-stat does'nt return any data.

Bellow an example :

$rp = Get-ResourcePool -Name "XXXXXXXXXXXX"

$todayMidnight = (Get-Date -Hour 0 -Minute 0 -Second 0).AddMinutes(-1)
Get-StatType -Entity $rp -Start (Get-Date).AddDays(-2) -Finish $todayMidnight.AddDays(-1) 

I don't understand why ...

For example, I can get performance data from Object VI : VM, Host but not for Ressource Pool.

Notice that I can see performance data from vShpere chart with no issue..

Hope my problem is clear and hope that someone know this issue.

Additional information :

     - vCenter / vSphere V6

     - Powershell v5