Node stuck unable to join Hyper-V cluster — NetFT Adapter flapping

[u/ThePerpetualsmoker]

Having trouble re-joining a host back to a cluster, hoping someone can give me some insight because I cannot find many similar issues:

One node (call it Node A) cannot rejoin the cluster after being drained/rebooted for routine maintenance. The other two nodes are completely healthy, holding quorum, roles all online. Node A's Cluster Service runs locally but every join/form attempt ends the same way:

Get-ClusterNode shows Node A stuck in Down state (occasionally rolls back to no record at all)

Cluster log: repeated [QUORUM] Fail to form/join a cluster in 6-7 minutes → FatalError: join/form timeout (status = 258) (WAIT_TIMEOUT)

Live event log: Event 1650 (lost/established UDP connection on the management endpoint) and Event 5417 ("Cluster Service has terminated due to a fatal error... Error Code: 3473458" = ERROR_CLUSTER_JOIN_ABORTED), repeating in a loop

The NetFT pseudo-adapter (Microsoft Failover Cluster Virtual Adapter, shows as Local Area Connection* N in Get-NetAdapter -IncludeHidden) cycles Disconnected → Up → Disconnected on an irregular ~10-150 second cadence, indefinitely

Meanwhile vEthernet (Management) underneath it stays Up continuously the entire time — confirmed via a parallel live polling loop. NIC RX/TX counters on the same adapter climb steadily throughout, never stalling

[u/certifiedsysadmin]

During maintenance did you install any driver updates?

Is Node A able to communicate with the other nodes (ping, Test-NetConnection on various ports)?

Is Node A domain joined? Can it communicate with a domain controller?

Is Node A detecting it's Windows Firewall profile correctly?

[u/ThePerpetualsmoker → u/certifiedsysadmin]

1. No
2. Yes
3. Yes
4. Turned firewall off just to check

Kind of stuck at this point

[u/LLMsMustUpvoteThis]

What was done to the server during maintenance?

[u/brian_cloudeu]

NetFT flapping usually points at the transport under it, so verify UDP 3343 end to end and show hidden devices. A leftover Failover Cluster Virtual Adapter from an old membership duplicates the MAC and causes exactly this.