Please make sure that VMs are not listed in Inventory node under added Hyper-V host. If you want to add second Hyper-V server you need to use machine's name (it wont let you to register the host with the same name twice).
Additionally when adding the machine via local host name check that you are adding the host using the local administrator account. Cheers!
UPDATE: From your video I see that Hyper-V is hosted on a Windows 10 machine and this version is not supported for backup. I'll discuss this confusing behavior with the team, but for sure it is caused by the unsupported Hyper-V version. Cheers!