Maybe this has anything to do with it?
https://support.google.com/googleplay/android-developer/answer/189724?hl=en
“Recent Changes are no longer managed on the Store Listing page. Manage your What’s New text from the APK page using the instructions above.”
[…]
“Text in the What’s New section may be automatically translated on Google Play. If you prefer to provide a specific translation for a given supported language, you must first Add translations for that language on your Store Listing. Once defined, you can choose the language from the dropdown and add the translation.”
The second paragraph seems to be overruled by the first, not sure what Google wants to say us with this. But maybe there is still something in the German store listing that prevents entries from the “APK page” to be used.
