Last month, a large number of artist entries were edited, seemingly in an automated fashion. Many artists with a pixiv link but without pixiv sketch or fanbox links, had sketch and/or fanbox links added. A large portion (possibly most) of these links are useless, leading to effectively empty pages. Pixiv may create "stub" sketch and fanbox pages for some or all accounts, whether or not the member uses those features. Whatever process was used to generate the links here grabbed links to these stub pages, even though they are not linked to from the main member page.
For example:
P.S. The fanbox links are slightly defective, in that a terminating backslash is omitted. Most modern browsers silently furnish the missing backslash; Firefox by default hides trailing backslashes entirely.