Setting User's Default Profile

I am an administrator on my community’s discourse forum. I am trying to set the system assigned profile picture so that the user menu icon appears. I have found the section under admin > settings > files that allows me to set an image URL. I attempted to set it to the default listed in external “/letter_avatar_proxy/v4/letter/{first_letter}/{color}/{size}.png”. This seemed to worked and displayed an appropriate image next to the “system assigned profile picture” option in the profile picture selection menu. However, when I select this option and hit save, it instead sets it to no image at all. When I go to change the profile picture again, no options are selected. I have no issues with setting a custom image. Thank you!