Not performing in what way? As in he's playing poorly or simply that he's not getting impressive ratings? Anchor man isn't really a role that tends to grab the best match ratings, as they are defensive specialists and their passing tends to be as simple as possible. Midfielder ratings tend to be based on key passes, which an anchor man shouldn't be making.
When you watch the matches, how is he actually performing? Is he able to effectively shield your defense? Do you get a lot of attacks throught middle past him? If not, he's performing the role as required.
If you want better ratings, you might want a more diverse role for him, such as Regista, DLP, etc. Those roles will make better use of his diverse skills.