I am seeing this problem as well.  As far as I can see, the code that parses the API into the HTML equivalent of question posts is looking for:

y.avatar.name,
// ...
y.avatar.imageSrc

While the API is populating "y" with something similar to:

{
    "avatarSrc": "https://cdn.kastatic.org/url_goes_here",
    "kaid": "kaid_goes_here",
    "nickname": "nickname_goes_here"
}

It also looks like the avatar name is located in another variable.