This is a problem I'm sure lots of people encounter, throughout the site and resources as the site gets older. Links start to evaporate and become broken. In our case it's because we changed our domain name & the root location of xenforo. Still absolute links stayed the same, it would be nice if we could do a find and replace on the content within the forums in order to fix these broken links, or alternatively just prune threads that are several years old. Best wishes.