While creating a custom Wordpress template, my site would crash when adding the search query string in the url. The url
website.com/ worked fine, but once it became
wordpress.com/?s=search+string it crashed without any kind of obvious errors.
The problem was happening because I never specified the Post Page from within the Settings > Reading section of the Admin site. Once I did this everything started behaving normally.
As usual, a really simple problem caused by my own stupidity. Hopefully this prevents you from spending way too long debugging the problem.