If someone searches for an invalid search, like
votes:twelve, those get silently discarded if they are paired with actual legitimate search terms. However, if those are the only search terms provided, then the search instead picks up every single living post on the site, it looks like. For example doing this on Stack Overflow you'd net about 18 million results out of questions and answers alike.
We've had other measures in place for other parts of search to prevent people from accidentally querying and grabbing the entire site, which I imagine especially on a giant like Stack Overflow, it's not kind to our servers to do those kind of things. I suggest that a search that only has invalid parameters be treated properly like an empty search string (which is that it returns nothing - or it could provide an error page as the old search used to).