Bug: Unlocking Tainted Eden in online play not giving achievement

[Facundo]

I was playing online with 3 other friends, and we were playing 3 Eden.
We got the Hourglass item on the first floor and used it to reach Home. There, the Red Key appeared in the chest in Mom's Room, so we opened the room and found Tainted Eden inside. We all unlocked the character, but the achievement didn’t unlock on Steam.
Does anyone have any clues on what might be going wrong or how to solve this via the console?

[kone]

I've also had issues with friends not unlocking tainted characters specifically. I doubt the creative method you used to unlock Tainted Eden would be the issue.

How we've dealt with it is having the person that has NOT yet unlocked that specific tainted character, be the host of the lobby.
When I (Dead God) hosted the lobby, unlocking the red room closet with the Red Key or the Cracked Key tended to fail all the other players from unlocking the tainted character, the achievement or both.

[Facundo]

So, you guys were able to unlock the tainted characters even though the host hadn't unlocked them yet? In our case, none of us had them unlocked, including the host of the game.

[Eri2c]

Open the stats page and go to secrets and it should update your achievements