You missed your opponent with a deathstrike
today I was fighting people on Siege Perilous and had deathstrike toggled but couldn't land it. At first I thought that maybe I hadn't pressed the right button or whiffed. However I did hit my opponent with a normal hit, so I didn't fail to hit and I was not parried, I did normal damage. Then I looked at my journal and it said "You missed your opponent with a deathstrike".
I run 120 ninjitsu and stealth and have never experienced this over the last 5 years.
Is this a bug? Or is this a nerf that was snuck in within the last day or two?