The automatic failover of primary and secondary DNS has failed

Question

Dear experts and support team,

Our server experienced a DNS failure last week. On March 2nd, all servers were unable to connect to the IP address of the DNS primary zone.

Both ping and tracert to 192.168.240.** failed, which caused the CRM server to be unable to obtain DNS information.

However, the backup DNS 192.168.247.** was accessible, but the server did not automatically switch to the backup DNS for resolution.

BTW, We have already properly maintained the primary and backup DNS information.

The CRM server is running Windows Server 2022 Datacenter, and the firewall has been turned off.

We are not sure how to analyze the cause of this issue. Could you please provide some suggestions?

Thank you very much in advance.