I followed the docs to implement the new adaptive icon by creating XML with <adaptive-icon> in res/mipmap-anydpi-v26/cs_ic_launcher.xml. The icon is correctly set in the manifest.
android:icon="@mipmap/cs_ic_launcher"
It all works fine when the app is installed from Android Studio. When I install the app from an APK, though, the default Android icon is shown instead on Oreo.
On older Android versions a correct icon from mipmap folder is used.
I analyzed the APK and the adaptive icon XML file was there but for some weird reason, the icon is not picked up when the app is not run from Android Studio (like by installing the APK from the command line or via a distribution service like HockeyApp).