Because I used the Google Maps Module instead of the Google Maps Widget I first missed the documentation about changing the Google map markers. But even with the documentation I do not seem to get the markers changed. I have created an enumeration with the appropriate icons. I have set the Enum attribute in the Appearance section and filled the Enum based marker with objects. In firebug I can see the references to the enumeration and the images, but google still displays the standard marker. Anything else I can do to check if I made a mistake somewhere?
Sadly, I can't really say much about your predicament without seeing a test project. Have you tried updating the widget from the App Store?
It might be something changed with icon loading/paths one of the new Mendix versions, but I'm not aware of any.