WHEN MW2 IS BACKWARD COMPATIBLE

Black Ops is backwards compatible so it will work on the One, but MW2 is not. You can see all games that are backwards compatible here - https://majornelson.com/blog/xbox-one-backward-compatibility/

You can play Black Ops online on the One and you would be playing with 360 and One players.

Yeah, one of the few COD's I may consider playing again.

I personally think they should remake it, as well as making it backwards compatible. They should at least remake it, though. MW2 deserves to be remade more than CoD4 deserved it.

My point is that it was announced 5 months ago that it would be coming so that means 1. Activision and treyarch already agreed to it with microsoft for releasing it for backwards compatibility 2. That means they have had 5 months to get the game ready which
is over enough and they said there starting with the most popular titles and most voted and there making the worst games backwards compatible and bo2 red dead redemtion mw2 bo1 cod 4 are all top voted games and none are backwards compatible

not sure if this pertains to your issue, however there maybe some correlation to what you maybe going through. I play COD Modern Warfare and I had the same issue were I wasn't receiving xp for the weapon. I found that there was some form of action in the
game that doesn't clearly state that if you have a special version of the weapon, then you don't get the xp.

I would try taking the weapon out of your loadout, applying a different weapon, and then make several loadouts with the same weapon your trying to get xp for. That way when you die, grab another loadout and see if that will cancel the bug if there is one.

Some COD games have very specific but unclear way to gain xp per weapon.

in the new game I knifed several players and got 0 xp for the weapon until I went to a standard knife with no skins, no blueprint.

Good luck.