Looks like the method creates the group in Manager mode.
Afaik VMW advises not to mix both modes for creating objects, see When to Use Policy Mode or Manager Mode
Btw, this Get-NsxtService cmdlet is deprecated.
You should use the cmdlets in the VMware.Sdk.Nsx.Policy module.
See an excellent write-up on the subject in PowerCli 13 Create NSX Security Groups
