I'm in the middle of creating a ticket.
Yes mounting is slow... But that value fixed it in version 8... It just needs to wait longer before the Helper instance responds.
23.05.2016 13:41:17 Error Failed to retrieve FLR appliance IP address Error: Timed out waiting for FLR helper appliance to respond. Possible causes:
1. Appliance is configured to run on different network than backup server.
2. Appliance is configured to obtain IP address automatically, but DHCP server is not available.
EDIT: to clarify this only happends with large VMs (2,8TB)
Small VMs 50-250gb work perfectly fine.