Tahm Kench cannot Devour Singed?

I play a lot and I've noticed in multiple games that he is sometimes unable to eat . I have never played Singed myself so I figured he simply had an ability that could negate/make him untargettable or something, but after asking other players, I was informed that he does not. I've noticed it a couple of times in team fights, but it is more noticeable when playing top lane Tahm versus a Singed because it is one on one. While fighting this match-up, I've noticed it many times.

Has anyone else had this problem or even noticed it?

It's been awhile since I've played vs but considering I haven't read anything about it in the patch notes, it has yet to either be noticed or taken care of.