Starcraft 2 For a Few Swarms More achievement

On the mission Last Stand on Legacy of the Void where you have to hold out for so many zerg, I’ve done this mission twice, I’ve saved it at 2.2 billion and I’ve ended the mission just after 2.3 billion and also just after 2.4 billion to be sure and it won’t complete. I’ve double checked it’s on normal mode, made sure it was over 2.3 billion, and still won’t complete. It’s a 10th anniversary achievement and I’ve completed others recently so I’m not sure why it’s not completing. Is it bugged?