Melee champions idling
I've seen this happen a few times with different champions, and only with melee champions so far. A melee champion will start moving into position to attack an enemy, but the other champions will arrange themselves to the chosen target can't be reached. The melee champion will then just stand there idling until the chosen enemy is killed, or until a path opens for the melee champion to reach the chosen enemy. This happens even if there is another enemy that he could be attacking during this wasted time, which is just silly. If a champion's target becomes unavailable, they should look for a new target immediately, and only idle if there are no targets available. While idling, they should also check for a new target whenever any champion moves or dies.