We say the device have the value 4 for a fan level and i try to publish value 3 i see the value change in iobroker webUi (no sound of device) for 2-3 seconds and jump back to 4, but if i change it manually in iobroker webUi i hear a sound on the device and its working.
Same problem when i try to publish with MQTT Explorer
If you only use Homey to send a message through the MQTT Client app, and the value jumps back, the problem is not in Homey. There is no automated action/flow in Homey that would revert the value back to its original value.