Zryas grasping roots not grabbing sometimes

I have had a few instances where enemy champ is under tower and Zyras grasping roots went right through them but did not grasp them, no they did not have banshee's veil. very frustrating. Sry i do not have video showing this.. if it happens again i will send vidieo, but as it stands right now i do not want to play her because this is happening i