I don’t see how it is a bug. It’s based on RNG better yet, luck.
I have only 2k hours played, I rarely fractal but I do WvW time to time. I mainly help others in Dungeons & roam PvE & I could care less for a pre or legendary, yet I was attempting to make the Delusion staff & on my 1st try at the mystic forge out popped the Legend – I don’t think everyone is guaranteed a pre & hours clearly have nothing to do with it for the most part.