Originally Posted by
Pavol Stromcek
The cassette didn't appear worn, and this was the mechanic's opinion as well. He said the cassette didn't need replacing, so in a way, it might kind of be on him.
I agree, doesn't look that worn. IME, chainsuck can be quite mysterious and unpredictable
and can include loose chain jamming between the lower jockey wheel and the RD cage.
Anyway, the point was that there are possibilities that don't involve error on the mechanic's part.