So, doing bounties, Paths of the Drowned, I found a red resplendent chest. Clicking it didn't produce an event or anything, but I was overrun with boggits. After they were all dead, just behind the chest, I saw a speech bubble over a blue boggit, with the text of the subject line. The boggit disappeared after, I think, less than a minute. The chest was clickable, and I got treasure. But neither this site, nor google, came up with anything on a search, and the blizz forums found 1 post, from 2014 (which I posted on), which means it's not a new thing from 2.4.1.
I had something similar OP; on the south entrance of the necro event in A2 stinging winds, there was what I thought was a cursed chest. I clicked it, I think some enemies appeared? But they vanished and there wasn't any loot.