The issue happens because users implementation for awaiter is buggy.
Users code relies on completed event of the AsyncOperation returned by UnityWebRequest. That event is fired when operation completes, however, you have to connect a handler to it before operation completes.
In users code two operations are fired and then awaited, so UWR operation completes before it is awaited due to playfabTask taking longer. If playfab task is removed, UWR task can be awaited.

Change UnityAsyncOperationAwaiter constructor as below fixes the issue for me (note, that Editor gets stuck in a loop after this change, since there is no exit from it).

public UnityAsyncOperationAwaiter(IAsyncOperation operation)
{
if (operation.IsDone)
{
IsCompleted = true;
_continuation?.Invoke();
}
else
operation.Completed += OnOperationCompleted;
}