Not attacking bug
Now before you judge right off of the title I'd like to clear up what this bug is; it's not the mechanic where you have a crap ton of melees and only so much space for them to attack (hence why they stop attacking and wait for a spot for them to poke into to attack)
This bug is when literally the champion just does not attack. It's placed on the field but it just stands there taking damage. I've witnesses three instances of this happening (none of them being me)
Once it happened on the first level where they had a warwick and it wouldn't attack the minions. The minions killed the warwick and the person took 4 damage.
Twice it happened when people's units were just standing there with only one on each side of the battlefield left. One unit would be attacking the other (it was a vayne and warwick again I think but this was a different game); and the vayne kept attacking the warwick but it would just stand there not doing anything and taking the damage which resulted in a lost round