Bard versus Spell Shelds
Bard's Q will still form a tether to targets that blocked the ability with a spell shield - meaning they are still vulnerable to being stunned.
Given the recent suite of changes you made to spell shield logic to make them behave how "players would expect", this feels like an oversight. While I'm going to assume this follows the same logic as Leona's E-dash or Mundo's Q-heal (i.e. effects that occur after hitting a target regardless of whether or not it's blocked), in the instance of Bard - being tethered sounds like an effect that shouldn't happen. The other "secondary effects on hit" all affect the caster, not the target. He should behave more like LeBlanc's E - which doesn't still tether to targets who block the ability.
That said, I also think that "blocking Leona's dash" is something players expect to happen when they negate Leona hitting them. So from the perspective of "what players expect", most of those "on successfully hitting" interactions should be disabled versus spell shields.