I tried binding another key, it didnt work at all for some reason.

Then i messed around with the presets and finally set it to ArmA3(which it has been all along), and now it suddenly works like it should.

Talk about weird.

Still no fix and the release is getting close.

There really needs to be a melee option. To this day armed forces around the world are trained in what to do when/if your weapon jams or you are out of bullets. There is also the problem of silent sentry/patrol removal (no not sneaking up on someone that´s waiting for something to happen, thats makebelieve unless he´s asleep, but if you are stationary and he´s walking right past you...)

A rifle is dangerous even when jammed or empty. You now have a heavy spear and/or club to use against enemies. If the enemy still has bullets and sees you coming.. you die.

A knife in the hands of a trained professional is a very dangerous thing. Thrust in and slash on the way out in the right spot and it´s all over, very quickly.

The melee should not be a stupid cod/bf instakill from any angle and distance though. You need to be properly placed and the physics need to be realistic. If your target moves, you miss. If your target has a modern ballistic vest with "plates" your attack on that part of the body should be ineffective.

On the other hand, if you manage to get behind your enemy within arms-length the kill IS easy. There is no real "countermeasure" to something like that, that´s just computergames bulls*it.
Human reactiontime is too slow for you to be able to counter a knife struck to the side of your throat (or inbetween your ribs, your kidneys etc). Forget "timed events" where you counter that attack with Hollywood-ninjaskills, no such thing is possible in real life even if you are from the SAS or Navy Seals. If they see you coming.. that is a different matter.

Only possible defence: don´t get attacked from behind in the first place.