[gameplay] Tahm Kench, selective eater? (Devour ally not working)

I've had on multiple occasions where attempting devour on an ally has NOT worked, I can't figure out why but it's becoming an increasing frustration. It doesn't seem to have a rhyme or reason, but I think it may have to do with displacement abilities (IE a dash, jax jump etc). I think if tahm tries to eat a champ in the middle of a dash it denies the W, but also locks it up until the ally uses the ability again.

I'm just throwing out a thought on what might be happening, but please look into this!