On one of our recent projects we had an issue where the Drupal site search was not working. There was a search.html file present in the home folder to handle a Google custom search page outside of Drupal. Since the filename was not the same as the drupal search path we did not expect it to be the cause for the Drupal search to not work.
What was happening was that Apache mod_negotation was mapping the requests to /search/node to /search.html/node because the path /search matched to the search.html file in the root folder.
This was fixed by turning off option multiviews for the directory which disabled the content negotiation in Apache for the directory and made the search start working again.
The following line was added to htaccess to achieve this
Hope this helps.
If you run into problems with Apache or Drupal you can reach out to us