I'm sure there is a thread about this already. I've played games where my tanks wont attack enemy structures without doing it manually. They will kill any movable units but not structures. Also I played a game where my units wouldn't attack the commander. Catapults wouldn't fire at him either. I had the enemy commander surrounded in 100 tanks, even right clicking on him did nothing.
more information about this would be great, if he was under their level, then that is understandable, like for example in a crevasse. tanks cannot shoot units in the water either. but again this is alpha so that's why you're here. If you know that there's already a thread on said subject, please post there and don't make a new thread, it will not reduce your chances of being answered, on the contrary. To report bugs here's where the magic's at : http://pa.lennardf1989.com/Tracker/index.php
This happens a lot around factories. The attackers are targeting a unit that is being built but won't fire until it is complete. Of course it also happen when an enemy attacker will come in range and they do nothing. Heck, in one game two groups passed thru each other with no firing.
you both need to report it at http://pa.lennardf1989.com/Tracker/index.php and make sure to try 5 or 6 search keywords before concluding that you are the first to report the bug. talking about bugs on the forum is taking to the wind.