I had a similar issue this evening when going from a level 40 alt to a my main who is currently working on Karma for a legendary.
The first thing I did upon logging on to my main was get 25 stacks of Luck, and then I hit some DE’s for about an hour. I have 60% MF from my gear, 40% from food and a banner, then 150% from the stacks of Luck. 250% MF, and I did not receive a SINGLE rare the entire hour I was on my main character.
I don’t know if there’s been a stealth nerf or what, but I find that DR absolutely horrid. The only thing I can think of is that I came from an alt, because there have been other times where I receive 3-5 rares within the first 20 minutes with that much MF. This isn’t a “give me my shinies” post so much as a “I’m playing the long-term grinding mats/currency for my legendary” post, but it seems day to day that ANET makes it harder and harder for those behind the curve to catch up.
K <><
