The Modbus to MQTT firmware version 1.3.2 factory default is to publish only when there is a change in the data.

If data is no more transmitted and data transmission becomes heartbeat packet (as below screenshot)

Changing <Publish> option from “Only when register value changes” to “Always” then the problem should be improved.

It is also recommended to have the <Retain> option box checked, so that the MQTT Service will save the last data, and publish the last data immediately when a new MQTT client connects and subscribes to this topic for the MQTT client, no matter whether the Modbus to MQTT Gateway publishes this information.