How to reproduce the error:

1. Select File >New File or Project >  General > Qt Quick Application - Empty > Choose to create a new empty project.
2. In the Screen01.ui.qml file, select Text and change the font size in properties to 24.
3. Select the Live Preview button on the toolbar.

The following application errors are displayed:

Starting C:\QtDesignStudio\qtdesignstudio-1.0.9-20190204\qt5_design_studio_reduced_version\bin\qmlscene.exe...

QML Debugger: Connecting to socket C:/Users/xxx/AppData/Local/Temp/QtDesignStudio-vTdYVB/qtcreator-freesocket.xZNWyg...

file:///C:/dev/tqtc-plugin-qtquickdesigner/studioexamples/examples/loginui1/loginui1.qml:8 Type Screen01 unavailable

file:///C:/dev/tqtc-plugin-qtquickdesigner/studioexamples/examples/loginui1/Screen01.ui.qml:14 Property has already been assigned a value

C:/QtDesignStudio/qtdesignstudio-1.0.9-20190204/qt5_design_studio_reduced_version/bin/qmlscene.exe exited with code -1