An odd thing regarding Guard Shell in X6 is that if you get a shot reflected with it and then weapon switch in some way or execute a giga attack right after, the weapon drain will instead happen to the switched weapon.
However, while this is nigh unnoticeable in most cases as most giga attacks fully drain upon usage and weapon energy is pretty plentiful, on top of it being hard to run into a situation where you actively use Guard Shell alongside other weapons, it just so happens that the Nova Strike is affected as well, stopping you from using it after the initial usage unless you get hit, use an energy restore of any kind or just die/exit the stage/go into another area that resets your ammo.
I've actually found out about this only because of Hell Sigma, as he tends to spawn a ton of aimed shot enemies at low health and I use Nova Strike to dodge his "USERO" attack, which is exactly what got me once and allowed me to find out about this glitch.
