Now it is the second time it happens that the search cannot return any results. This hickup is rare but it happens. To solve it I had to follow these steps:
- Stop the Timer Service
- Clear the configuration cache
- Find in ProgramDataMicrosoftSharePointConfig the folder where the file cache.ini exists
- Delete every file from this folder EXCEPT cache.ini
- Open cache.ini, delete the content and put ’1′ (without the quotes) in it and save the file
- Restart the Timer Service
- Index reset
- Full crawl
Source: ITIDea. The linked blog post saved my afternoon today. Thank you, Anita Boerboom.