Monitoring LLD discovered alerts and how to recover when they clear

[arusso]

We're trying to monitor a UPS system via SNMP where an alert is exposed in an SNMP table and when it is cleared it is removed. We have been able to successfully discover alerts as items and triggers to alert at a certain level based on the data returned, but we're struggling with how to get those triggers to resolve.

Once the alert clears the UPS it is no longer exposed via SNMP and LLD will mark the item as no longer discoverable. In this state, the trigger remains in the PROBLEM state and does not clear despite a few attempts (it's almost as it is not evaluated again once it is not found anymore).

I have tried updating the expression to only the trigger if data has been received in the last 5 minutes, but that doesn't seem to work and the trigger does not seem to be evaluated further once the item is no longer discoverable.

How do I get the trigger to recover when the underlying item (alert) goes away?

Here's the discovery rule:

key: xupsActiveAlarms
oid: discovery[{#ALERTID},.1.3.6.1.4.1.534.1.7.2.1.1]

the alarm severity item prototype:

key: xupsActiveAlarms.AlarmSev[{#SNMPINDEX}]
oid: .1.3.6.1.4.1.534.8.1.1.2.2.1.5.{#SNMPINDEX}

and the trigger prototype expression:

{ZBX-POWERWARE-UPS:xupsActiveAlarms.AlarmSev[{#SNMPINDEX}].last(#1)}=1 and
{ZBX-POWERWARE-UPS:xupsActiveAlarms.AlarmSev[{#SNMPINDEX}].nodata(300)}=0

Thanks!