Since the latest patch, it is impossible to obtain driller king bags, and the farewell letter drop rate is much lower than usual. About 1-2 weeks ago, I have done the letter quest in about 15-20 mins, and only got a few more of the other letters than farewell. This time: I don't think this is normal. I have also drilled on the whole map, the only area which seemed to have them (very sparsely) was the southwest one, near the portal. And again, while I have drilled up all these letters, used up a whole basic drill, I have found ZERO driller king bags.