Tahm Kench W bug (spitting out things)

I was playing a custom match to test out my internet connection so that I don't disservice anyone with disconnecting on them. So I decided to play Tahm Kench, but while I was playing him I noticed that every once in a while his devour ability wouldn't spit the minion/monster back out and it would say that it was on cooldown during the time that the enemy was in him (never happened when i cast it on a champion, but I also didn't devour many champions). So basically it went from the 6 seconds to spit out a minion/monster (which i sometimes couldnt cast out as I wanted to) to 6 seconds it comes out towards your next autoattack victim and then on its full cooldown right after.

this is on the live server