I play with zane. Sometimes, while playing the game, it is impossible to use it even though the number of shoulder canons is still charged. Is it a bug?
It is a little bit of a bug, every now and then I find when I use it too much it just stops letting me use it.
It can be easily fixed though, by going in to your skill trees, equipping a different action skill, exiting your menu, waiting a couple seconds, and then going back in to re-equip the cannon. Then you should be able to use it again.
Stop spamming busspoy