Since the latest security update of Nov 2017, Cortana 2.9.7 en_us apk stopped working. Its window is closing and it's logging me out each time . I installed the APK not from the play store, but it used to work until now. I tried everything, uninstall reinstall, nothing works. So, no cast, no Cortana, I think I should go back to my old Lumia 950.