Rank lock was a myth created by kids who couldn't accept being incapable of getting a 50. I had no problem getting to 50 after 6000+ mm games in Halo 3.
You were always rank locked in H3. I had to get a new account because I was playing with really good people and we won like 12-14 games in a row. It ranked me up to a 48 which I am not. Got a new account and stayed at 36 where I belong.
I'm asking you to elaborate more. Is this a result of a specific mechanic that 343 Industries has implemented and talked about, or did you just lose a few games, noticed that your rank wasn't changing, and came to the conclusion that you are permanently rank locked?
It's just that it doesn't make sense for them to keep you at a rank permanently for losing a couple of games. That's not how a ranking system works. However, Rank Lock as a result of the system's certainty about your rank was a thing in Halo 3, and it might be what they are experiencing here.