Hi,
Generally you get this event log when IP address of the SNMP server not being configured in the device configuration.
Please refer this KB article:
# https://kb.juniper.net/InfoCenter/index?page=content&id=KB26262&actp=search
As you are trying to poll via the internet, it would be coming from NAT IP address. So, hope you have configured the NAT IP address in the community configuration.
Even after this you are facing the same issue then I would suggest you to log a case with us (JTAC) we will troubleshoot this issue further.
Regards,
Rishi