DNS cluster member(s) not reloading?

I know I can create a ticket for this, but first I just want to know if there are any known issues that are being addressed so far. I've got a DNSOnly cluster with four members; two CentOS 6 servers (ns1-ns2), and two CentOS 7 servers (ns3-ns4). When I edit a zone, the update is pushed to all members. I've *never* seen an issue with either CentOS 6 server, but I've got issues with ns3-ns4. One of them, ns3, works fine most of the time, but ns4 will always fail to reload BIND. So I can update a zone and only ns1-3 will show the new serial number until I restart BIND on ns4. Restarting BIND will immediately result in the proper serial number, every time. Resources are not an issue, and all four servers are running 70.0.48 STABLE. Anyone else?