The issue is that on four routers we can't get SNMPv3 to authenticate. The other Juniper routers are authenticating correctly with identical config. The Zabbix host profiles have been cloned from other working profiles (IPs and hostnames changed to prevent conflicts) so it is unclear what the issue may be.

Steps to reproduce:

1. We have stripped and reapplied the SNMPv3 config on our Juniper routers. 
2. I have manually configured the engine_id to ensure there was no conflict and regenerated it to ensure that it stuck. 
3. I have manually checked the engine_ids of other Juniper routers to ensure there is no conflict.
4. I have checked and double checked that the authentication details configured for the host on Zabbix are identical to what's configured on the Juniper router.
5. tcpdump has only shown "authorizationError[errorIndex==0]"
6. wireshark packet inspection has shown a get-response with error "authorizationError (16)"