Issue's been mentioned already in bug report on forum twice and feedback thread on reddit, most active gunners on discord reported experiencing that issue as well. Too bad it's still now acknowledged in known issues thread.
It feels extremely punishing on gunner, especially in PvP where it basically means you're dead, since ss and hook are a main way for gunner to iframe and are timing based, in PvP scenarios you're bound to have a really tight timing between noticing someone's dashing to you etc. and you reacting to it with a hook and even if your reaction is fast enough you still get cced due to iframe not being there at the beginning of your skill (while it should be there) and on top of that you get punished since ss goes on cd and in case of hooks you lose a charge. It happened multiple times in every 6v6 game I've played since the update.