Categories disappear

This is an issue that I’ve been having that is starting to get really annoying. All of my categories will disappear. They won’t show up in the categories management page, or on the posts. All the posts display as being uncategorized. If you try to go to an archive page of categories it says that it doesn’t exist. The thing is that they will randomly come back. After they come back they will go away again. If anyone has any ideas about this it would be greatly appreciated.