I feel a bit sorry for this as I've discovered the issue that lead to this new behaviour in 9.5, but it's way better as it is today, trust me. As Alexander suggested, the solution to use multiple appliances is to setup the appliance to use DHCP, and in order to unmount a FLR is to logoff from EM, or to wait for the timeout, that is 20 minutes of inactivity. I'd go for dhcp to be honest, so you don't have to worry with manual umount or limits of FLR's that can be used concurrently.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1