Identify any hosts that have been improperly added to or removed from the cluster that still have vSAN enabled but with no network connection to the other cluster members.
These can be identified via the vSphere client and validating that only the hosts that are part of the current vSAN cluster and have vSAN network configured appear here: Datastores > vsanDatastore > Hosts
If extraneous hosts that should not or do not have access to the datastore are listed then these still have vSAN enabled, this can be disabled via SSH to the host:
# esxcli vsan cluster leave
If you are unsure about making changes, please make changes during maintenance windows, if possible, or do consult VMware Support with the respective severity. Leaving hosts or changing the membership list can cause cluster partition and objects to go inaccessible.