Android x86 Build error: QML import could not be resolved in any of the imort paths

[randsfjorden]

Dear Community,
right now I try to build my QtQuick-Application on Android x86 to publish it on Google Play. Don't panic, the problem discription is not as long as it looks like. Below I just describe my installation and what I have tried so far.

The problem is that every time I try to build the app, it sais
BUILD SUCCESSFUL

Total time: 18.125 secs
Android package built successfully in 25.810 ms.
-- File: D:/Dokumente/Qt/Workspace/build-Wadden_Sea_Dictionary-Android_f_r_x86/android-build//build/outputs/apk/android-build-debug.apk
Warning: QML import could not be resolved in any of the import paths: QtQuick.Controls.Material.impl
Warning: QML import could not be resolved in any of the import paths: QtQuick.Controls.impl
Warning: QML import could not be resolved in any of the import paths: QtQuick.Controls.Universal.impl

Even though it sais that the Build was successful, it wasn't because of the warnings (when I run it in a virtual machine, the app is all white). I really have no clue what to do. In another forum I read, that the app is white because of the warnings (but I couldn't solve the problem with the hints given there, this is why I ask here).

The App runs perfectly well on Windows and Android armeabiv7a, it even runs well on mac and iOS. My building environment is Windows 10 with QtCreator installed (Qt 5.8, newest version of all compilers and Qt-components, android x86 with gcc 4.9). Qt is not installed in a Location that contains whitespaces, and I reinstalled the Android x86 compiler several times. Android Studio and NDK (newest version) are also installed, and they run as I said perfectly well for android arm. I shortened the build path, so that it is not over 256 characters long.

The weird thing is that this error even occurs when I try to run a test-application (just the standard QtQuick-default-application). When I change the style to universal in that example application, i get other import errors, but it still doesn't work. In the android x86-folder, the Material folder is in exactly the same location as the android-arm folder.

I hope you can give me a hint about how to make Android x86 work :)

Thank you in advance, randsfjorden