Trace one point from the bus to the subscriber

1. Check SB1000's broker connection status. In MQTT mode, Modbus polling pauses while MQTT is disconnected. A broker/network problem can therefore also remove the expected RS485 polling traffic.
2. If disconnected, check the configured URI scheme, destination port, network/DNS, credentials, broker access rules, and any TLS requirements for the selected transport. Do not include secrets in a support report.
3. If connected, verify the serial port is in the intended MQTT mode and that the required device and point are configured. Save pending profile changes and allow the protocol service to restart.
4. Inspect the exact published topic/prefix and subscribe to the configured topic. Confirm the subscriber is observing a new live message rather than a previously retained value.
5. Inspect the source device/point diagnostics. Check its Unit ID, serial settings, function/address, type/order, and scale. A broker connection alone does not establish a valid Modbus read.
6. Review publish/poll settings and the device's update rate. A point configured as write-only does not supply a freshly polled measurement; firmware 8's history explicitly separates write-only handling.

Do not change wiring solely because a disconnected broker stopped the MQTT driver's polling. First restore the missing connection, then verify the bus evidence.

Expected result

One configured point produces a fresh message with a value matching a known field reading. If not, include broker status, redacted connection details, exact topic, point definition, source error, and firmware version.