In the attached reproducer, there is a Worker filling a ListModel to display a keyboard.
If you click 3/4 times on the button, it will either crash or infinite loop.

Some error cases possible:

• The rowModel becomes randomly a "TypeError":

  js: populate QQmlListModelWorkerAgent(0x55a80667b140)
  qrc:/qt/qml/BugWorker/virtualkeyboard_worker.js:24: TypeError: Property 'append' of object TypeError: Type error is not a function
  

• sometimes, it will freeze just before displaying this log.
• other mention a QWaitCondition:

  js: populate QQmlListModelWorkerAgent(0x5649c5d90ca0)
  QWaitCondition: mutex destroy failure (Device or resource busy)
  qml: triggered
  

Maybe not related to this issue, but as long as there is a Worker in the main.qml, there is this warning at the application start: qt.core.qobject.connect: QObject::connect(QJSEngine, QtObject): invalid nullptr parameter