Tahm Kench W (Devour) Bug

I played a few games as tahm kench and I was going against a rengar top and I wasn't able to eat him at 3 stacks. Lost the lane because of this. Yes it was off cooldown and he DID have 3 stacks of an acquired taste . Then it happened again later today when I tried to W a lulu, again with 3 stacks, and it didn't work.

Am I the only one getting this or am I missing something?