Well when I click my "Toggle Weapon Mode" (The key that switches between ranged and melee.), sometimes it doesn't work. For me it's set as "Q", because it's easier and faster to press than "X" for me. So when I press it, sometimes it doesn't work, requiring me to press it repeatedly until it does. It's not just the key either, I'm able to use it fine in other activities (Most notably, typing and other games.). This is a minor inconvenience, because usually when I enter melee I can back up for the several seconds I need to press the key repeatedly. But when I'm surprised or in very close quarters, it can be the end of my avatar's life (I use avatar meaning as the character you're playing as.).
Other keys I've tried using are; "Tab", "E". I want to use a key that I can access quickly because, sometimes you aren't expecting melee combat and it's a surprise. I'm fine when I have a secondary item though, mostly a sword or sabre briquet.