so I've pulled the mystery box like... 10 times and every time I got the is this a bug? it's kinda annoying :p

I think it's because there are 65 items restocking in Cavern of Curios and only four of them are rarity lower than 66 :(

This is not a bug just an unfortunate day. As stated above, there are so few low rarity items in that shop that you will mostly get the hookah.