This occurs on my laptop that requires pressing a Fn key to enable the Function keys. The Show Hitboxes key combo F3+B does not work if the Fn key is also being pressed. The only way I have been able to get it working is to let go of the Fn key and immediately press F3+B. As far as I can tell, the other debug key combos work fine, although I have been unable to get F3+Esc working at all.