Getting 'Validation of Active Directory Failed" error. Also cant add the node by Computer name like "COMP-NAME" in cluster validation windows gives and error that "The Computer COMP-NAME could not be reached"

I have 2 nodes(sql server 2016) and 1 AD/DNS...
Firewall is turned off on all the servers
able to telnet, ping, nslookup on all the servers to all the other servers
they are added to the same domain, failover cluster is installed in the 2 nodes

It throws the error "The Computer COMP-NAME could not be reached" when i try to add by browsing the 'computers' in the domain.. (it recognises the computer name in the domain when i browser) but its not able to add that computer.. it is able to add itself.. ie node-1 can add its own comp.. node two can add its own comp but not eachothers.. I can add both of them by IP or FQDN though... but even then the cluster validation fails with 'Validation of Active Directory'..

Im sure its not the firewall issue, not able to point out the error here.. please help