Thresh not being able to hook Sion while in passive [gameplay]

During a game last week I found 2 separate examples of Sion not being hooked while he's in his passive by Thresh. As you can see in the video I posted, in both situations the hook hit and dealt damage; however, it just hit the ground rather than CCing the Sion.

In that game i was able to recreate the bug 100% of the time; however, I have not had a chance to try it again another game.

1. Play Thresh against Sion
2. Kill Sion to activate his passive
3. Attempt to death sentence Sion while his passive is active.

Thanks and feel free to reach out to me if you need any further data.