[GAMEPLAY] Can't eat friendly Graves with Tahm Kench

Hello,

Last game I played Tahm Kench support and I could never use my W on my friendly Graves. I tried everything, but i couldn't eat him in any situation. I only encounterd this in my last game, I tried it again in a costum game but then i could W a graves. I don't know if there is an option for a player to disable it, so that other friendly players cant eat you or something else like kalista ult? if that is so i would like to be informed