Steps to reproduce:

• Create a new Host
• Add a SNMP Interface
• Create a template where you define the Macros needed for the interface configuration but forget to create the “{$SNMP_CONTEXT} macro
• Add some SNMP Agent Item to the Host
  
  Result:
• The SNMP Interface will become “Not available” with a timeout error: “Timeout while connecting...".
• If you click on the SNMP Item on the host and click “Test” the item works and you get a value back, since device is configured without context name.

This is caused by the fact that in the SNMP Interface configuration in the “Context name” field the macro “{$SNMP_CONTEXT}” is set, but this macro has not been defined on the Template or Host
What seems to be happening is that for “normal” SNMP Items checks Zabbix is sending the Value {$SNMP_CONTEXT} as context name since the macro has not been defined, but when manually testing the Item Zabbix seems to not send this context name → this is inconsitent und leads to confusion while troubleshooting because the interface gives a timeout error while a manual test works just fine.

Documentation:
https://www.zabbix.com/documentation/current/en/manual/config/macros/user_macros

If Zabbix is unable to find a macro, the macro will not be resolved.

Expected:
Consistent behaviour of the undefined macro - no value or macro name returned and also described behaviour in the documentation.