Hi Folks,
The reported observation could be due to stp loop. There are occurrences of STP loop which intern introduce flooding of control traffic in the box. Look for STP loop and DDos logs in the box.
Junos OS Distributed Denial-of-Service (DDoS) protection identifies and suppresses malicious control packets while enabling legitimate control traffic to be processed.
Couple of commands to check the DDOS violations, [verified in MX Platform]
show ddos-protection protocols statistics terse
show ddos-protection protocols statistics brief
show ddos-protection protocols statistics detail
show ddos-protection statistics