I checked, and for some reason this may be a client side glitch.
I wish. As soon as I noticed it I logged off the server, went on singeplayer, and it was on instantly, same with other servers (completely forgot to mention this, sorry). But when I joined that server, despite it saying in text "hitbox shown". it wouldn't display a hitbox on anything (items, mobs, my player in f5). I even asked 2 other members on the server to F3 + B and they said nothing happens, but the owner said it worked just fine for him
I'll send a screenshot at some point