We are aware of this extension issue. It's ultimately due to a known issue with iOS that we’ve filed with Apple.
In the meantime, what you can do to correct it, is the following:
1. Disable Nomorobo in Settings
2. Force-quit (swipe up) Settings
3. Uninstall Nomorobo
4. Reboot your phone (hold down the power button)
5. Reinstall Nomorobo