Active Manager is in an unknown state on server 'DR-MAILBOX-002'. Basic database administrative operations such as mounting or dismounting and the ability to have failovers or switchovers is not available. EXCHANGE 2016

Question

I have exchange server DAG running exchange server 2016 CU 19. In primary network i have two mailbox servers and in DR, I have two mailbox servers.

primary mailbox servers and one DR mailbox servers are working fine each with health copy of the databases. databases are mounted in primary site.

One of DR mailbox server stopped working. In ECP it has a status of "operational" set to NO. I don't know what happened.
No database copies in that server except the one that were previously created.
Checked services, all microsoft services are up and running, except for Cluster service which is missing in that server
Failover cluster manager does not even discover that server for me to select it

I checked on event logs and i didn't see any logged errors.
Removed the server from the DAG then re-added it, still same issue.

When i run the command below in that server , i get error displayed. What is the main root cause of the issue and how can i resolve it.

`[PS] C:\Windows\system32>Test-ReplicationHealth
WARNING: Server DR-MAILBOX-002 is part of a database availability group but it does not host any replication-enabled
database copies. Only system-level diagnostic checks will be performed.

Server          Check                      Result     Error
------          -----                      ------     -----
DR-MAILBOX-002      ReplayService              Passed
DR-MAILBOX-002      ActiveManager              *FAILED*   Active Manager is in an unknown state on server 'DR-MAILBOX-002'.
                                                      Basic database administrative operations such as mounting or
                                                      dismounting and the ability to have failovers or switchovers is
                                                      not available. Review the event logs for more details. Error:
                                                      Unable to access cluster root key (Error: An error occurred
                                                      while attempting a cluster operation. Error: Cluster API failed:
                                                      "OpenCluster(null) failed with 0x6d9. Error: There are no more
                                                      endpoints available from the endpoint mapper")

DR-MAILBOX-002      TasksRpcListener           Passed
DR-MAILBOX-002      TcpListener                Passed
DR-MAILBOX-002      ServerLocatorService       Passed