I just found out that if fancyhdr has to mention a chapter located in \backmatter, it does this by numbering it with the number of the last chapter. For instance, this: \documentclass[11pt, a4paper, ...
I am trying to get a simple on every page but excluding title page. Now I only get footer in front matter and excluding title page. The main matter do not get footer. Edit: I want a simple footer ...