MQTT packets not detected

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Hi Guys!

I am running a capture to track a condition between a PLC and broker (PC on my desk) using my laptop to run wireshark on the same LAN as these 2 devices.

I am using VNC to operate the PLC's HMI display and can see these packets, however I cannot see any MQTT packets (connect request, publish, subscribe) even though I can see successful comms.

I do have MQTT as a protocol with port 1883 and it enabled in the Analyze>Enabled Protocols menu.

Any ideas on what I may be missing? I can ping the broker and the PLC and see successful request/response.