Bard ultimate doesn't stop Sion Ult or his passive in time.
Im just a Sion main ( not a Bard main ) and I notice this. Sion ult can't be stopped by bard ult I believe.... happen 2 times and both times couldn't be stopped. Also sion in his passive mode can not be stopped too , he loses hp even when he gets freezed by Bard ult.
Sion ult is called unstoppable charge so it makes sense. But idk bout his passive. Bard should be able to stop his health decay. This works for both ally and enemy bards btw.