Back when 2.0 launched the game had a massive surge of players playing SMN and SCH since they were the new jobs. Both of them are pet jobs and pets used to be affected by the debuff on Locksmith and the last boss that required you to eat fruit to cure it; unfortunately the player eating fruit didn't cure their pet so the pet would always die.

Pretty much every party back at 2.0 launch would have a SMN or SCH and so every party would struggle massively on Locksmith and the last boss due to the bug killing pets. That's why the dungeon has such a reputation. They fixed that bug a long time ago.