This issue affected v1.0.38 of the Android/iOS app with routes that are very long (e.g., cross-country). We made a temporary fix by reducing the map line quality on long routes. We also released a new version of the app v1.0.39 that fixes the issue. The map line quality will return after affected users have updated to v1.0.39 or later.
Please try to update the application to the latest version. Contact support if you are still experiencing any issues.