Since the latest update game progress VERY frequently gets stuck. Sometimes when rolling back to the previous area after a wipe your crusaders will no longer do any damage and be invisible with only the buffs showing until monsters start damaging them. Then they get wiped again but instead of rolling back to the previous area the monsters will just keep on walking through instead of turning back after reaching the left edge. At this point frame rate drops to like 1 per second, or less. This is happening with the "gray goo" objective, no idea if any others are affected or if it is limited to this one. It's rather annoying as it requires a restart for the game to progress any further which wipes any partial progress of the current highest area.

Playing on Steam.

This is what it looks like at the infiite walking stage after the second wipe:
http://images.akamai.steamusercontent.com/ugc/437236976017516996/726F2CD55E33D78FE9C8A107EDBCF4F0F450B706/
Note how Draco shows as alive despite being rather dead.