To reproduce: launch mapviewer.

Then this dialog pops up:

Microsoft Visual C++ Runtime Library

Runtime Error!

Program: E:/Qt/Examples/Qt-5.9.4/location/build-mapviewer-Desktop_Qt_5_9_4_MinGW_32bit-Debug/debug/qml_location_mapviewer.exe

This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. 

                                                                                                                                    [ OK ]

The other examples (so far) of the 5.9.4 package starts fine, so it seems to be specific to the mapviewer example.