your propeller has a rubber holding to the shaft that is broken (not really but its slips).
Take the propeller out of the shaft, you will see how is making the connection between the propeller and the shaft.
You have 2 ways to repair it:
1. To bay a new propeller...the best solution.
2. To make the holes diameter 3mm or 4 mm, at 120 degrees 3 holes, in the metal part when you watch from the front and with special instrument make the treads M3or M4.
Then do the montage – propeller on the shaft, and tight the special bolt
with hexagonal head
, to hold the propeller to the shaft without slipping.
This solution is temporary, because the bolt that you tight can broke also...