NOISE drops out when your iOS device's screen goes on Auto-Lock, i.e. when the screen goes dark.
When using NOISE, especially during a live performance, we recommend that you adjust your Auto-Lock activation settings.
To do this, go to your iOS Settings and select Display and Brightness:
Then adjust the Auto-Lock setting – while the Auto-Lock setting will save your iOS device's power, you can set it to Never during your performance.