Reproducer with sample index.html attached. First, start a local server (python -m http.server 8080 or something similar) at the location of index.html and then launch the reproducer.

One should be able to confirm 2 things:
1. WebChannel works fine. Message is echoed between QML and JS. That means "registerObject" works well.
2. "registeredObjects" is an empty array, despite the fact that the object is in action already.

Solution: use "WebChannel.id: <id>" + "webChannel.registeredObjects.push(<QtObject>)" instead. Documentation says that "registeredObjects" is read-only - that is not true.