18.1.7 insight report no data for openvpn

[c-mu]

Hey,
i have a few interfaces in my setup and i'm able to collect much data for all them except of the openVPN Interace. I allways get the message "No Data Available". Please have a look a the attachment.

What I have done so far?
Rebooted the system,
restarted the services flowd_aggregate and samplicate

checked, that the openvpn interface is listed in netflow.

thanks for any advice!