Roomba j7+ I have just gotten error 30 this morning and worked fine then at 9PM it's happened 3 times and I've emptied the bin, cleaned the sensors. 90Seconds later it appeared.
iRobot Roomba Bumper Sensor repair - Schneor Design and More
iRobot Roomba cliff sensors - Solve Error 9 - Circle Of death Issues - Used | eBay
iRobot Roomba 500 Series Error 9 Troubleshooting - YouTube