You should probably change the propellers. I had the same problem, with propellers that didn't have any visible problems (like scratches). After having them all changed, I was able to flip Tello.
The funny thing is that there weren't any black propellers available, so I bought the Iron-Man version. My Tello is a bit ugly now but it flies perfectly and does all the tricks.
I thought the same, I had a hard time looking for the black propellers when they fell out.
I hope it will be easier with the reddish ones. But they haven't fallen out yet!