Tahm Kench Devour (E) not working on some allied champions

(In title i ment W not E*) I was playing as Tahm and noticed one game that I could no Devour my ADC Graves, I got him to try standing still to no avail. Sadly the issue lasted all game and did not end there, next match I was not able to Devour my allied Fiddlesticks, one more was my friendly Gankplank. It seems to be just one champion per game but is seemingly random, but one champ per match it seems I am unable to Devour. It still allows me to W then click them but there is no animation or effect at all and it acts as if I am selecting a invalid target