Bakugo, Shoto, Ochako, Iida, Yaoyorozu, Kirishima.
Kaminari, Jirou, Ashido (fought the League and helped poison Giganto, and we saw Kaminari's thoughts, he loves Jirou + Ashido only remembered Giganto when she saw him in the forest).
Tokoyami, Mezo, Tsuyu (had fights with the League and Shigaraki would have decayed Tsuyu, no way he'd do that to a friend).
Literally the only possibilities would be guys like Sero, Koji and Hagakure. And Aoyama was semi-debunked already. I don't see any room for a traitor in Class A.
I'm not big fan of MHA, or not fan at all, but Hagakure was always number one in list of possible traitor/spy from the very begining. She like always was behind scene in major battles. Maybe her power is one that AFO gives her(which means she has more)...but still hard to understand what was goal of traitor from the very begining.