What's the cause of `cannot convert to a HexString`?

Problem: Alarms with event reasons Invalid SNMP Criteria: cannot convert to a HexString appear on several different hosts. It’s the default SNMP monitor. They get resolved automatically in further polling cycles.

Expected outcome: Maybe not throwing alerts that I can’t interpret or an alert with more helpful information.

OpenNMS version: 28.0.0

Two SNMP monitor issues in one week. Maybe there is a relation to What the cause of '.�{�t�.' does not meet criteria'?. But as I said, we didn’t update the components.