WW/Voli AI Not Attacking

Short and to the point: I've noticed that sometimes (particularly after casting, from what I can tell) Warwick and Volibear will just sort of stand around, not attacking or moving even if there are open tiles to move through or an enemy adjacent to them. They'll stay that way for the round. This has happened frequently enough for me to notice and I've only seen it happen to these two, but I've seen it occur multiple times. I really couldn't say what was causing it as I haven't noticed anything distinct about the occurrences yet. I don't know if this is a known thing or not - I imagine it is - but I decided to post it anyway just for posterity's sake.