Some time when trying to add already joined node to new hyper-v cluster you can error like :
“The computer hyperv-node-server-name is joined to a cluster.”
This can happens when you changing cluster on the domain or trying to fix a broken cluster . In order to clean the node from left over cluster settings you need to run on the node it self as administrator :
Import-Module FailoverClusters Clear-ClusterNode
After running the above you will not having any problem to add the node to a new cluster !
Good Luck