[GAMEPLAY] Poppy's Ultimate Snapcast Knockup Bug

I've had a number of times where I've used Poppy's snapcast ultimate to knockup an enemy champion but the knockup just doesn't occur. The ability will connect, deal damage, etc but instead they'll just appear to be very briefly suspended far less than the usual knockup time then walk away as if nothing ever happened. Xerath and Yasuo are the only two champions I can currently recall happening to so I'm not sure if it's champion related or not.