On EX4400 series switch, there is a software bug which some SNMP trap would not be generated properly when FAN try is removed and inserted.
This KB describes the details of this bug and provide the details.
On EX4400 series switch, it is expected to generate SNMP trap below when FAN try is removed and inserted.
FAN 0 removal:
jnxFruRemoval
jnxFanFailure
FAN 0 insertion:
jnxFanOK
FAN 1 removal:
FAN 1 insertion:
jnxFruInsertion
However, it doesn't work as expected when using a certain Junos version.
The affected SNMP trap are jnxFruRemoval and jnxFruInsertion.
The issue has been fixed in PR1687848 partially and PR1726908 completely.