Check the output of the "cluster status" command from one of your CVMs. Also, you may want to run a health check on your cluster to see what it reports. Its likely as @sverhoevne mentioned, prism needs to be restarted, but it would be good to check to make sure that's the case first.
You can put Prism Central into its own VLAN, as long as you have routing and the appropriate firewall ports open to connect Prism Central to the Hypervisors, CVMs and IPMI. Generally I stick with putting the Prism Central into the same VLAN for simplicity sake.
For a Hyper-V host, it is meant to be run with SMB storage. You could generate an iSCSI volume with ABS, but I don't believe this would be the best way to handle storage for a Hyper-V host. https://portal.nutanix.com/#/page/docs/details?targetId=Web_Console_Guide-Prism_v4_7:wc_block_services_volum...
I appreciate the response @lapfcukle, but that's means I need to go buy a certificate from a CA. Using LetsEncrypt enables me to get a free, valid certificate. I get valid certificates from LetsEncrypt, I just need to know how to convert them to a format that Prism Central/Prism Element can use.