So I recently ran into this issue with the Twitch mobile app on a samsung galaxy s4 phone.
In order to fix this blank login screen I had to go to the app store and update "Android System WebView"
Direct URL Link:
https://play.google.com/store/apps/details?id=com.google.android.webview&hl=en
Upon installing the update and trying the Twitch android app again, the login screen worked and I was able to get into my twitch account.
Other options you may consider if still having problems.
- Uninstall and reinstall the latest twitch android app
- Make sure to delete all cache from the app in settings
