I've implemented the following for the Photon-Playfab merging. It works in the editor, but in the WebGL build, the callbacks (both) for the method are never executed, and the game gets stuck after. Could it be a potential bug? Thanks a lot for your time!
PlayFabClientAPI.GetPhotonAuthenticationToken(new GetPhotonAuthenticationTokenRequest()
{
PhotonApplicationId = "SOME-HARD-CODED-ID"
}, AuthenticateWithPhoton, DisplayPlayFabError);
Please make sure the PlayFabClientAPI.GetPhotonAuthenticationToken method has been executed. If not, the callbacks certainly do not execute. You can add some debug statements to confirm whether the method is executed. 
