If you are seeing notification tickets that cPanel DNS server is not able to contact one of the web servers on 2087 with "no route to host", make sure that IPTable rules on both servers have allow rule for port 2087 and test via telnet, one to the other, on port 2087:
ns1: telnet web1 2087
web1: telnet ns1 2087
On the web server you can check and try re-enabling the cluster DNS server, if disabled due to too many failures. Search "cluster" and look for Cluster DNS.