I have this V8 site with a somewhat big database. Searching the individual categories like "Articles" is no problem, but when searching the entire site, this happens:
I managed to track the problem to the forum search include, where $fieldsvar (which is used in both queries, effectively turning them into monsters) yields this:
I don't know why they're there, but they've been around since 8.00.19 on Github, and removing them fixes the issue. They reset the $swords-array which is used in the search_querylike()-function, rendering the latter a (useless) monster in the forum and every other big table.