After upgrading the agent to 3.2.0, we see issues with discovery (some hosts discover no interfaces, others discover correctly).
Also seeing net.if.in/out returning an error.
Running the zabbix_agent as root has no effect on the behaviour.
Although it does appear that igb1 is in kstat:
Agent 3.2.0 failing to return interfaces in discovery:
I believe this is somehow related to