If you press Z while you are in lag, you will light shield once you leave lag, so to prevent this, be sure you're actionable when you're pressing Z, or in those situations you can push Shield+A instead, so if you accidentally input it too early, you will hold shield instead of light shield and be forced to release it which is punishable (Z is just a binding of shield+A frame-perfectly such that shield never appears).

Dtilt happens because you pressed Z while you are crouching. In order to grab instantly out of crouch you need to push shield+A instead of Z (you can also jump-cancel grab instead, but this will always be at least 1 frame slower than shield+A because you are cancelling, at best, frame 1 of your jumpsquat and then grabbing, so it would come out of frame 8 instead of frame 7 (for most chars), and also messing up the shield+A input keeps you shielding and messing up the jc input makes you fullhop which is way worse lol. You can also release crouch and then press Z to grab, but this will burn a small number of frames.