Odd problem with core search: no results

Dear Drupal Community,

I’m experiencing an odd problem and it is totally possible that I am missing something trivial, but I’m stuck (and searched thoroughly) and would appreciate any nudge in the right direction:

I’m using the default core search and don’t get any search results.

• The website is indexed 100%, there are 0 items left to index.
• The search index table is filled.
• Active search modules are „Node“ and „File Entity“, „Node“ is set as „Standard“
• Cron ran.
• Caches are cleared.
• Permissions are set for guests and authenticated users (every role is allowed to use search)
• Error log does not show any errors, only the default notice, that someone searched for a keyword.
• The database user has all privileges including CREATE TEMPORARY TABLE (GRANT ALL PRIVILEGES…).
• I already deactivated and uninstalled the search module, ran cron, cleared the cache, reactivated everything, configured everything and the website is — again — indexed completely.
• I tried the „Custom Search“-Module with the same result.
• Status report does nor show any errors or problems.
• Website is not in maintenance mode…
• Neither files nor node search get any results…
• …and yes, the website actually has lots of content :D

Drupal Core: 7.41

I never experienced any problems with the search function and I host a couple of websites with the same provider, using the same drupal core version, where search functions as desired — what the heck am I missing? I’m at a total loss.