1. Error message
2. Reasons
This is because the custom mode is selected when using mqtt.fx. The software remembers this configuration and does not completely clean the configuration when reinstalling or uninstalling
3. Treatment method
Modify the configuration file
Path: C:\users\{administrator user name}\appdata\local\mqtt FX
the following: mqttfx config.xml
Modify: modify custom to light
<styleName>LIGHT</styleName>