Someone deleted the AUTOLINK BB-Code from your installation. It actually should not even work in forum posts without the BB-Code, but it's possible that cached links from before the tag was deleted will still appear.
Create a custom BB-Code named AUTOLINK.
With the tag missing, the tag is not added to the parser's tag list, which is the same effect as disabling the tag in Syntax Manager. Thus it is working as designed that autolinks don't work when the tag is unavailable.