Sounds like a circular error with monitoring is flooding their network with metrics and logs, causing DNS to fail and produce more errors, flooding the network. Likely root cause is something like DNS conflicts or hosts being recreated on the network. Generally this is a small amount of network traffic but the LBs are dealing with host address flux, causing the hosts to keep colliding host addresses as they attempt to resolve to a new host address which are being lost from dropped packets and with so many hosts in one AZ, there's a good chance they end up with a new conflicting address.