Hello
Thank you for your question and reaching out. I can understand you are having issues related to S2D validation failed.
Some items to note here for troubleshooting further.
Patch the All Nodes with all Windows OS Updates and reboot them.
Try disabling the Antivirus on both the servers and give it a try.
Please check from Storage and SAN end if all connections and Disks are good in heath
Here is a thread as well that discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
Cluster Network Validation - fail UDP port 3343
https://learn.microsoft.com/en-us/answers/questions/249241/cluster-network-validation-fail-udp-port-3343.html
S2D Cluster Validation Fails Firewall and UDP Port 3343
https://social.technet.microsoft.com/Forums/office/en-US/c3e15170-2a83-48a8-b671-efc2a9afe4cf/s2d-cluster-validation-fails-firewall-and-udp-port-3343?forum=winserverfiles
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