App crashes when using QtBluetooth in DLL

I'm having a library for all communication stuff, including Bluetooth.
Any application trying to use this library will crash during startup.
I'm not expecting the functionality to work on Windows7, but I was able to run the Application on 5.4, but 5.5 will fail completely.
On OSX the same code works fine, also (slightly modified) on 5.4.

The crash happens inside LocalDeviceRegisterMetaTypes() when trying to register the first MetaType "QBluetoothLocalDevice::HostMode", while getting objectClassName().

Screenshot attached.