WiFi settings, iRobot app bugs, or login difficulties could be the cause of your Roomba i3's inability to connect to the app. To quickly reestablish the connection, restart your robot, update the app, check for 2.4GHz WiFi, and try pairing again. https://roombasmarti.com/ultimate-guide-to-troubleshooting-and-maintaining-your-irobot-roomba-i3-plus/