A number of users reported some issues with NuDroid in the last few weeks. Please update Nudroid now.
It is available on Google Play. You can also download the APK from here: https://github.com/Cybnate/NuDroid/releases/

The release fixes the following issues:

•    A fix for styling problems on some devices mentioned here: https://discuss.nubits.com/t/nudroid-v4-now-available-on-google-play/2436/6?u=matthewlm
  
•    Show error when a Shapeshift transaction fails after pressing Send.
•    Do not stall the Shapeshift update timer when leaving the application.
•    Improved shut-down of the Blockchain service, making certain parts of the app more responsive and fixes an Application Not Responding problem that mostly occurred whilst restoring wallet backups.
•    Do not close the app after restoring a wallet whilst inside the app.
•    A few rare crash bugs, and a few code improvements.
•    Also fixes an additional issue with restoring wallets.
•    Added a secondary server by default improving the resilience when the primary default server is not available.

Do you need support or have questions? https://gitter.im/Cybnate/NuDroid

Or checkout the videos:
1) The Power of NuDroid (6 minutes) Link: https://youtu.be/E0YyRX8tnHI
2) Getting Started with a Mobile Wallet (10 minutes) Link: https://youtu.be/DYfemvz2xDU