I believe a made a post similar ages ago, but it seems this achievement is still not tracking your Frontline wins if you are not tied to your original Grand Company that you chose when you first started the game.

Some info: Originally was Immortal Flames, switched to Twin Adders months ago. Today, queued at 164/200 wins, won a Fields of Glory match as a freelance for Immortal Flames, still at 164/200. Please fix pretty please