It's an A/B test which is completely random. Unfortunately, you were part of the "random" set of users that didn't receive lingots for your streak. ;(

As said by Plyze, it's an A/B test. See here.

Before I stopped getting my streak lingots around day 180, I had never (since my first few days on DL, on a travel day) missed a day. Since then, I have missed three days (and spent 10 lingots for the streak freeze to preserve my streak). This is anecdotal evidence that the streak lingots are a "gamification" motivator to keep me coming back to the site consistently.

Six months, no missed days. Six weeks, three missed days.

I agree that it's probably an a/b test. I'm in the control group: have some lingots.

I'm not getting any lingots for my special 500 streak ;(

Same thing happened to me. How can we recover them?

I had been getting my streak lingots through day 60, but did not get it for 70 or 80. Would the A/B test be instituted at any time? Will it ever change back? Maybe if I drop my streak and start again? If anyone knows, please explain.