So did you executed pvecem delnode <oldnode> after you removed the node?
If not gain temporary quorum with
pvecm expected 1
pvecm delnode old-node-name
If you have done this and it does not work please post output from pvecm status
If you just added the Agent option in the VM, you must fully shutdown the VM and start it again.
Agent option creates a hardware device on the VM. This device is not hot-pluggable.
Blockbridge : Ultra low latency all-NVME shared storage for...