I have encountered a similar problem, which has not been resolved. However, your example does not illustrate this issue.I test the example ，when myModel = newModel，print myModel.length =0

I know I'm too late, but...I was also interested in this problem and found the following in the qt source code:

The difference between a GeoMapObject and a MapItem is twofold. First, GeoMapObject are always backed
by a plugin-specific implementation and do not come with a default implementation. If a plugin does
not support a specific GeoMapObject type, adding such a GeoMapObject will have no effect.
Second, GeoMapObject are not QQuickItems, thus being a much more lightweight way to add content to
a map.
GeoMapObject support is plugin-dependent, and is documented per plugin.

Thanks for your efforts.
As you said it works in a project I have a second look at my code.
I'm not writing a Quick-App but a QWidget-App and use the map inside a QQuickWidget. I have read about another approach to embed qml content in a QWidget-App using QQuickView inside a QObject-Container.
This approach works as expected. I don't know why it doesn't work with a QQuickWidget but my problem is solved.

Best Regards

Has any one experienced the same problem ? Any idea of a possible workaround ?
Thanks for your help.