There's rare as in "hard to find," and then there's rare as in "nonexistent." Some players were wondering which one Khorium, a new mineable metal in the expansion, and the rarest metal in the game, was, after a few of them leveled all the way to 375 mining without seeing one node of it pop up.
Neth first said it was spawning as normal (very, very rarely). Apparently it's a rare spawn from Fel Iron or Adamantite nodes, but players just weren't seeing it come up at all, or seeing it come up very, very rarely-- as in one node every few hours. Finally, earlier yesterday, Tseric acknowledged that the rate was spawning lower than intended, and a hotfix was planned and pushed. When players still complained that they weren't finding it, Tseric said one more fix was on the way, and so Khorium should now be back in the game and spawning as normal.
Now, fixed in three days isn't bad for a bug, and now that it's back in the game, there's really no problem. But didn't anyone in beta hit 375 mining? How did they not catch this one?