New Addon domain/sub domain not getting DNS

I have a few servers, one of which serves as a DNS server. I configured clustering with this DNS server. My other servers were functioning properly, and I recently added a new server which has been running smoothly for almost a month. However, I suddenly encountered a DNS issue with this new server. When my users in cPanel attempted to add an Addon domain or any subdomain, the domain didn't go live. While the DNS server showed that the domain had DNS, a check on a DNS checker website indicated that the site was down and there was no DNS. Strangely, when I configured the cluster with a new API, it worked. But This is Temporary. Note: My server provider had briefly shut down this server two days ago for an hour, and the issue started after that. I've tried various fixes, but nothing seems to work permanently. I'm seeking assistance to resolve this situation.