I have searched the Zabbix bugs/issues and this issue has raised its head quite a few times in past versions and despite SNMP validation being put in place, the issue persists.

Its a similar case to that if a polling iteration has been missed, the next iteration is completely skewed, going from ~1Kbps to ~333.72 Tbps.

I am not seeing any unsupported notifications in the logs when this happens but i am still investigating why a poll is missed on occasion and whether this is network or Zabbix related.