In such cases close the game and then use Rejoin button. It happened with me a couple of times. The bug occurs when game has found while connecting to hero lab/other match (to watch)
I was also thinking that we need an upgrade for the Tankbuster. But I would do just same thing devs did to Cooldown. Just add hp percents to damage (make it 10-12%) and lower the charge time. Name it something like Tankslayer.
Motivation: just not enough damage in late stage of the game.