Currently, the user's Discord avatar is stored as a direct URL to the Discord resource. But if the user changes their profile picture, the resource is no longer valid.
The Discord avatar URL scheme is https://cdn.discordapp.com/avatars/<user_id>/<filename>.<extension>, where the filename can change at any point. This causes the image to not render (shown below).
To solve this, the Discord user ID should be stored, and then from there the avatar should be fetched with the Discord API.