[Gameplay] Tryndamere Ult Bug? Maybe?

I was playing as Tryndamere and I was running away a "gank". I got pretty low on health, so I used my ult, think it would keep me alive long enough to escape. The auditory cue for the ult starting went off and... I died. I was killed, I assume, by the enemy Annie's projectile. However, I was in the Baron pit when I died so i could have been killed by him, though I don't remember hearing or seeing him getting aggro'd. The main point is that Tryndamere's ult was someone bypassed and I died when my ult should have kept me from dying.

This is the first time that I definitely activated Tryndamere's ult and died during its duration. There have been a few times when I thought I hit my ult quickly enough before I died, but I am unsure if it actually went off or not.

As I was so shocked at my unexpected death, I didn't look at exactly what killed me or anything unusual that happened, other than the death. As I do not know the exact circumstances under which this happened, I doubt that I can repeat it at will.

I hope that this was an isolated incident that will only occur under unlikely circumstances. As someone who has played Tryndamere a lot, I rely on my ult's consistency to allow me to play more aggressively. If the ult is now unable to consistently give me more time to live, then I fine it a deterrent to play one of my favorite champs.

If anyone has any idea why this happened, or if something similar has happened to you, please comment. Thank You.