The following warning is logged. Since there is no message with ID 0, it should not be requested for retransmission.
WARN [org.jgroups.protocols.pbcast.NAKACK] (OOB-19,10.1.1.1:55200) (requester=10.1.1.2:55200, local_addr=10.1.1.1:55200) message 10.1.1.1:55200::0 not found in retransmission table of 10.1.1.1:55200:
[0 : 7 (7) (size=7, missing=0, highest stability=0)]
It occurred during a FLUSH when a node is trying to join the cluster, in a network that is dropping some multicast packets.