If you run into an issue where one or more of your loadouts has reset in Modern Warfare 2 or Warzone 2, unfortunately, you'll have to recreate it from scratch. As of right now, there is no universal fix from Infinity Ward to address this problem.
The only loadout pieces you can buy from Buy Stations (now referred to as Shops ) are primary weapons. It will cost youR$5000 (in-game, of course) to buy your primary weapons from a Shop. That's a big change from Warzone, which allowed you to buy your full loadout from any Buy Station forR$10,000.