aside from the multiplayer issues, i think the most gamebreaking issue players face is the targeting bug. a lot of us have encountered it, and i'm sure it's been talked about a lot. i fix it by quickly right clicking ground and then hitting the ability again, so if anyone has a quicker method please inform.
as far as i can tell, the bug is random and occurs when a player hits a hotkey to active an ability, left clicks his/her target, and the ability does not trigger. instead, the player's DG will likely stand doing nothing, even upon repeated activations of the ability. the only way to fix the problem is to make the DG perform another action, such as moving, and then retry activating the ability. if i knew how to reproduce the bug exactly, like maybe it occurs when you're sending too many commands or changing destinations a lot prior to hitting the ability.
this has occured to me with just about every DG. i've seen some older threads, even some more recent beta threads (march), talking about this issue but trying to isolate it to specific DGs. i'm pretty sure it's just a global bug. some examples: i missed a kill with pounce on a UB because my DG did not perform her ability when I hit the hotkey and left clicked UB (she just stood there, didn't even keep chasing him). i've had people die/almost while i tried to get my heal or bramble shield to unbug (the most frustrating thing i've experienced in-game). i've had people slip out of range while fireball wouldn't cast. i could go on, and hell, i think this bug might even occur when targeting DGs to simply auto attack.
imo, this bug needs to go immediately. it really makes the game feel unpolished whenever it occurs, which isn't rare, at least in my case. the only thing that might contend with this bug is the pathing issues that DGs clearly experience when traveling to destinations and targets (easier to reproduce than the targeting bug).