Your Roomba i3+ Evo's cliff sensors are detecting a drop, causing it to bump the edge. First, ensure the Home Base is placed at least 4 feet (1.2 meters) away from the stairs to prevent falls during departure and return.
Clean the four cliff sensors on the bottom of the robot with a clean, dry cloth. Do not spray any cleaning solution or water onto them.
For a permanent solution, establish a barrier. Use the iRobot HOME App to create a Keep Out Zone along the stair edge. Alternatively, use the Dual Mode Virtual Wall barrier in Virtual Wall mode. Place it at least 8 feet from the Home Base, positioning it to block the stair opening.
If that didn't work: Excessive sunlight or very dark flooring at the stair edge can interfere with the cliff sensors' infrared beams. You may need to adjust the barrier's position.
Heads up: Always use a physical barrier for balconies to prevent access.