Mine suffered from the same fault. It was caused by a circlip behind the gear that drives the blade coming off. Unfortunately to get to this I had to take the motor off, take the blade off, and unscrew the two screws that hold the blade drive in place (you can leave the two smaller screws in place as they just secure the bearing). These screws are thread-locked so they take a bit of persuasion to move. The circlip is easily reattached with a pair of circlip pliers.
Reassembly is the reverse of this but it is tricky as there are a multitude of wires to get caught.
It took me quite a while to do this job. FYI I’m just a DIYer and the job needs no specialist skills, just patience!
Not sure how long the fix will last but it’s ok for the time being.