Hi cestarik,
Based on the description, this looks like a firewall signature log, not a TNI error.
During SNMP discovery, TNI sends SNMP v1/v2c and/or SNMPv3 requests to devices. Firewalls may interpret these queries as unauthorized SNMP access and trigger signatures like HP.OpenView.Hidden.SNMP.Community.Unauthorized.Access.
Check the event details on the FortiGate. If the source IP matches the server where TNI is installed, this behavior is expected during scanning. If the firewall is blocking the traffic, SNMP discovery may be affected. In that case, add an exception or whitelist rule for the TNI server, or adjust the policy for internal SNMP scanning so these queries are allowed.