Port EventLog Repeated NULL for some parameters

I have been getting alarms on port threshold reaching 90%. When I go to device and check the graphs I cant see any reason for tghe alarm. Except that in the port eventlogs I see some of the port paramters repeatedly switching to Null and back, like below:

Timestamp Port Event
2019-11-13 11:20:14 29 ifConnectorPresent: -> true
2019-11-13 11:20:14 29 ifPromiscuousMode: -> true
2019-11-13 11:20:14 29 ifHighSpeed: -> 1000
2019-11-13 11:15:24 29 ifConnectorPresent: true -> NULL
2019-11-13 11:15:24 29 ifPromiscuousMode: true -> NULL
2019-11-13 11:15:24 29 ifHighSpeed: 1000 -> NULL
2019-11-13 10:10:12 29 ifConnectorPresent: -> true
2019-11-13 10:10:12 29 ifPromiscuousMode: -> true
2019-11-13 10:10:12 29 ifHighSpeed: -> 1000
2019-11-13 10:05:23 29 ifConnectorPresent: true -> NULL
2019-11-13 10:05:23 29 ifPromiscuousMode: true -> NULL
2019-11-13 10:05:23 29 ifHighSpeed: 1000 -> NULL
2019-11-13 10:00:08 29 ifPhysAddress: -> 0409731cb323
2019-11-13 09:55:26 29 ifPhysAddress: 0409731cb323 -> NULL
2019-11-13 09:20:07 29 ifMtu: -> 1500
2019-11-13 09:15:23 29 ifMtu: 1500 -> NULL
2019-11-13 05:35:19 29 ifAdminStatus: -> up
2019-11-13 05:30:27 29 ifAdminStatus: up -> NULL

Could you please help me debug and find the problem here?

What alert rule are you talking about? Post your alert rule. So we can better understand what you are talking about.

SELECT * FROM devices,ports WHERE (devices.device_id = ? AND devices.device_id = ports.device_id) AND (((ports.ifInOctets_rate*8) / ports.ifSpeed)*100) > 90 AND (ports.ifOperStatus = “up” && ports.ifAdminStatus = “up” && (ports.deleted = 0 && ports.ignore = 0 && ports.disabled = 0)) = 1

Here is the alert rule.

The problem is those parameters changing to null and back.

I m guessing libre changes parameters to null when there is a SNMP timeout.