The Sledgehammer has become available for players to unlock through a Black Ops Cold War challenge. However, a bug is resetting player progress, stopping them from acquiring the melee weapon.
Black Ops Cold War x Warzone Season 1 is in progress, which means that you have many new weapons available to you. The Sledgehammer is the second melee weapon from Cold War that you can now unlock.
If you want to get your hands on it, then you need to a complete a challenge that has get double kills with your knife. The difficulty of this task has been compounded by a glitch that is resetting players’ progress without any prior warning.

Sledgehammer Glitch keeps resetting player progress
The exact parameters of the challenge require you to score 15 double kills with the knife in separate matches. Completing this in multiplayer, Warzone, or Zombies should unlock the Sledgehammer, but this…