If it's not DNS, then it has to be the network
A few months back, I came across a peculiar issue in my production network. We had 3 data centers with WAN links between them. Each had a Domain Controller with one location having two (A regular and a Read Only Domain Controller). One of my colleagues reported that there was an intermittent replication issue that was discovered only after one of the DC’s failed, of course, not long before my arrival.