[GAMEPLAY] Tham Kench W unnable to spit monsters bug

This have been happening to me sometimes. I play Tahm jungle and sometimes when i use devour (W) on a jungle monster the attack itself enters in cooldown, the full 14/13/12/11/10 sec. even before i spit the monster (regrugitate) and i cannot spit the monster until the cooldown is finished and then the cooldown starts again. i didn't noticed anything of this when i use W on champions. Because this is random and not allways happens i was unnable to take screenshots or video.