A. Check your app settings to ensure that the 'Stay logged in' option is enabled, if available. If not, try uninstalling and reinstalling the app to reset any corrupted data that may be causing the issue. After reinstalling, log in again and see if the problem persists.
B. Make sure your iPhone's software is up to date. Go to Settings > General > Software Update and install any available updates. Sometimes, app issues can be resolved with the latest iOS updates.