If you're experiencing app crashes, there are a couple of steps you can try to resolve these issues:
Close high memory apps: crashes on a mobile device are commonly due to high memory use, and closing background apps can help free memory. For Android devices, there are some step by step instructions at http://blog.laptopmag.com/how-to-close-android-apps, and for iOS at https://support.apple.com/en-us/HT201330.
Restart the device: restarting can also free system memory which may resolve the issue.
Update your operating system: there may be an operating system update that resolves the issue. For Android devices, you'll need to check with your device manufacturer (Samsung, LG, HTC, etc.). For iOS, there are instructions at https://support.apple.com/en-us/HT204204.
Free-up device storage: when a device is low on storage, your app could misbehave in a variety of ways. For instance, it may require the user to login much more frequently than normal, possibly even every time they open it! Review the usage of the device's storage and consider removing unneeded and unwanted apps, photos, videos, music files, podcasts, and downloads.
If your crashes are related to photos on Android, try reducing the photo resolution in your photos app. The below is an example of how to do it on a Samsung Galaxy phone. Other camera apps on other phones work differently, though most should have the option to change resolution. If you're capturing a large number of photos, you can also try lowering the Image Upload Resolution setting in the app editor in the UX > Options tab.
If the steps above haven't resolved your issue, contact Customer Support. When you contact support, please let us know which device you're using and what OS version you're running. For example, "Samsung Galaxy S6 running 5.1.1" or "iPhone 6 Plus running iOS 8.3".
It will also help us to know if the crash reproduces in a web browser on your device. To test, open Chrome on your Android device or Mobile Safari on iOS. From the browser on your device, login to appsheet.com. In the My Apps section of the website, click Preview for your app, then Fullscreen. This should start your app in your mobile browser. Use your app as you normally would and let us know if you see the problem while running in the browser as well.