Hello,
Do You see any "DDOS_PROTOCOL_VIOLATION_SET" entries in MX syslog? Such as
Mar 28 03:32:53 mx-re0 jddosd[2356]: %DAEMON-4-DDOS_PROTOCOL_VIOLATION_SET: Protocol resolve:ucast-v4 is violated at fpc 0 for 218 times, started at 2017-03-28 03:32:53 BST
The exact "protocol" may be different in Your case.
HTH
thx
Alex