Disruper lasers are not intended to use ammunition when you upgrade to level 3. But when you are out of Materia and ammunition, you can't use the disrupter lasers. Not supposed to do that considering it should be conserving and not using any ammunition. That way you wouldn't need to spend to get ammunition.
#Disrupter laser bug
silent cedar
hard wedge
I noticed the same issue myself today; It's incredibly annoying to get locked out of weapons firing because buddy decided he wanted to waste the ammo for the other guns.