Can not use -UpdateMembers Attribute

[Lukasb1109]

Servus, we are trying to add a new Safe with a Script User and then add a local Group to the new safe. After the script successfully created the Safe the group add fails with the message

"User or Group was not found. To automatically attempt to add use AddOnUpdate."

Command:
.\Safe-Management.ps1 -PVWAURL "https://%FQDN%/PasswordVault" -UpdateMembers -FilePath "C:\Temp\CyberArk\safe-members-sample.csv"

Group is defenetly created and can be authorized via the pvwa.

If we try the following command the add works fine:
.\Safe-Management.ps1 -PVWAURL "https://%FQDN%/PasswordVault" -Update -FilePath "C:\Temp\CyberArk\safe-members-sample.csv"

Is there any bug by the UpdateMembers parameter?

thanks in advance,
Lukas