When this happens, it’s because it’s trying to reference an old version of the page that you have saved on your computer, and it’s running into conflicting messages. You may have to clear your cache.
If you don’t want to go through these steps, or don’t want to lose your cache, then instead visit the site in Private Browsing or Incognito mode (Chrome Instructions / Firefox Instructions). You’ll have to do this every time though (until it eventually corrects itself), but at least this will tell you if that is the problem.
How to clear your cache:
Log out of this site, then navigate away from the site (go to Google.com or something). Make sure no other browser tabs have any pages from this site open.