Thresh Hook Can't Hit Sion Passive

I was playing an ARAM today as Thresh and the enemy team had a Sion. I kept trying to hook his passive form with my Q to help deal with it but every time I tried my hook would just stop short of him and disappear similar to when you try to hook through a Yasuo Windwall. I tried it quite a few times and every time the same thing happened. Flay still affected Sion's passive form fine and I could use Q to hook Sion in his normal form no problem.

I was using the Championship Thresh skin and I think Sion was just using the base Sion skin.