Okay, the issue seems to be Tryndy's spinning slash just does not work. Previously, I had experienced problems where I moved or targeted a position close to myself and it did not work. However, as of 9/28 (first time playing Tryndamere since the last patch), my friend and I have experienced an issue where the slash does not activate. My friend reported he was not moving, was target correctly, that it was even using his health without doing anything in terms of spinning or slashing. I did not believe him and attempted it myself. He experienced the bug three times in one game while I experienced it once.
How to reproduce
1. Load the PvP.net client.
2. Duo-queue into a 5v5 game on the default map (no winter version).
3. Select tryndamere.
4. Sit in bottom lane and spinning slash to a target opposite the direction Tryndamere is currently facing.
I'm not sure if the direction Tryndamere is facing is relevant, but the only time it happened to me that was the case! Hope this helps.