Special Characters Display as Codes in Posts and Post Titles
 

All the special characters inside forum posts and thread titles suddenly started to display as codes (for example, ¡ ). You can see an example post here.

Before that they were displaying perfectly. It looks like vBulletin started to escape the characters for some reason (& gets converted to & and thus special characters don't display correctly).

I am using VBulletin 3.8.6. How do I fix this?