Guild Wars 2

What there an explanation as to WHY the spider boss of TA UP Malrona’s projectile doesn’t reflect with any of the guardian’s and mesmer’s wall?

You were able to more or less insta-kill Malrona by utilizing reflections, and the devs decided that this was detrimental to the dungeon experience (or something along those lines). As such, they made it so that you can no longer reflect those things, meaning you can’t just explode her and move on.

I believe it was listed in some of the recent patch notes, but I don’t feel like digging them up right now.

It wasn’t and it wasn’t post in the Game Release Notes section. It was a stealth “fix” and I wouldn’t excuse the insta-kill as an excuse to remove reflection. This is like saying that there is no point in having reflection at all if a mob shot at you and it shot through it.