I'm 90% sure the problem is simply that URL re-writing is misconfigured. The real URLs for posts on sites like this all end in icky query parameters like ?thread=13445. To make the URLs look prettier (and be ranked higher in search results), it's common practice to implement URL re-writting to transform icky URLs with question marks and equals signs and all that glop into pretty ones with the names of things and without icky symbols. The URL re-writting happens between the request arriving on the web server and the web server fulfilling the request. I.e. the web serving part of the web server always sees the true URLs, or at least it should, and right now it seems it isn't hence so many links being utterly broken.
Assuming I'm right, the short-term fix is trivially simple - disable URL re-writting and make-do with the true URLs until the web server configuration can be fixed. I.e. change one setting in the admin control panel and let us all get back to using the forum, viewing ads, and generating revenue for the site owner!
Here's the relevant docs:
https://www.vbulletin.com/docs/html/main/options_seofriendly_urls