Hi @Marco Bakker,
Can you ping between nodes? Make sure that the fourth replica can communicate with the other three replicas and that all necessary ports are open.
Did you join the Windows cluster for this node? You can check the specifics via Failover Configuration Manager. The cluster log in there will record some error messages.
In the case of four nodes, you also need to configure the Quorum mechanism.
Windows Server Failover Clustering (WSFC) uses a quorum-based approach to monitoring overall cluster health and maximize node-level fault tolerance. A quorum node set is a majority of the voting nodes and witnesses in the WSFC cluster. The overall health and status of a WSFC cluster is determined by a periodic quorum vote. The four nodes will appear 2-to-2.
Please refer to this article:
In addition, here is a MS document:
Best regards,
Seeya
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