Sorry, I found the problem just now.After logging in,the wiki system displays the skin that users have chosen.In fedoraproject wiki system there are 3 skins for users to choose.the default one is called "Fedora".But now only the "Fedora" can be displayed correctly.
I used "Modern" one in the past,and now it seems missing something when being displayed(CSS?Sorry I can't describe it in more detail.I'm not familiar with this),so it displays just like a white paper now.
My solution is just change the skin,but I hope you can check the others and fix(or replace).
Thanks for your patience.
Ambassador/Contributor of Fedora Project and many others.