Before you start
If you have photos that are waiting to be uploaded, do not delete the app. They will be lost if they haven't been saved to your device, as they haven't had a chance to sync to the cloud yet.
Tap the Upload Status Queue on the app's home screen and save all photos to your device before deleting the app.
Troubleshooting steps
Try turning your device's Airplane Mode off and on a few times - give a moment each time you turn the mode on and off.
Hit Retry All by tapping the upload status queue > tap the Three Dots in the upper right corner > Retry All (leave the app open while they retry and upload).
If this does not work, tap the upload queue > tap the Three Dots in the upper right corner > select Save All.
Log out and log back into the app.
If that doesn't work, please hard close the app and restart it.
If that doesn't work, restart your mobile device.
The final thing is to make sure you can find the photos that you've saved to your device. It's now safe to delete the app and reinstall it.