Over time, deposits form under the propeller blades. These build-ups can lead to a blockage of the propeller. Occasionally, a piece of a printed part may also get stuck in a propeller and block it. If this occurs, you need to empty the purge bucket. Then, dismount and clean the propellers. This is really easy if you loosen the retaining screw and carefully remove it. Subsequently, clean the propeller and its support and mount the propeller back. You can find more information under in the user manual.