Okay so whenever you're using the 500 mm Canon there is a bug where when you load a different type of ammunition that is different from what is currently in the gun, that gun will stop operating until you manually remove the previous ammunition from the inventory...

So for example.

500mm casaba shells currently in use.

Cycle consumables used to select 500MM HE.

Guns stop fireing and stop tracking.

Force reload. No change.

Remove old casaba ammunition from inventory. Guns instantly load on their own and begin operation again.