It’s not just the Crimson’s Set. It started popping up randomly for several players since Patch 2.6.6 went Live.
The first one I saw was after killing Greed in a T16 Vault when I pressed the hot-key to open my Inventory.
The second one I saw was during a battle in a T16 Rift.
The third one I saw was during a T16 Bounty run in Act III.
