Slow mode doesn't work

Hey folks, I'm having trouble activating slow mode. I've turned it on in the settings, set it to turn on automatically when combat starts, bound it to a shortcut to activate manually, and nothing seems to work. There's no discernible change in the game speed and no visual cue that it turns on or off. I want it specifically for a few jumping puzzles and I cannot get it to work. I'm playing on PC. If you are able to get it to work, can you walk me through exactly what you did and what happens? No one else seems to have encountered this problem so I may just be missing something stupid. Thanks for your help