When your roomba stops does the “status” light or the “power” light turn red? Does it do any sounds or beeps after it has stopped?
When you say that you clean it thoroughly, do you clean it with compressed air? If not, it might be a good idea to do so. You may want to clean the robots cliff sensors, drive wheels and under the robots bumper with compressed air to see if this helps.
You may also try resetting the robot by removing the battery, pressing the power button for at least 15 seconds and then reinserting the battery.