with the previous FW,  there is no such error.  why after upgraded to 500.  immediately the motor speed error occurred.  how to fix it?

Hi there, to ensure a safe and enjoyable flying experience, we have added a new safety notification feature on the Mavic Mini in the latest v01.00.0500 firmware. This new feature lets customers know when propellers need to be inspected or replaced. Please check out this post for the solution https://forum.dji.com/forum.php?mod=viewthread&tid=214705.