Hi Stefano,
Thank you for the details. The configuration seemded perfectly fine, so I logged in via SFTP and debugged the query and the results. Interestingly, the plugin actually did return the correct results (including hotel Eden), so I checked if you have any custom filters in the theme functions.php file, that may alter the final results.
The cause is actually a custom code, that you have on lines 482-515 in the functions.php file in your theme directory. If I disabled it temporarily, the results were returned correctly again. It looks like it is used to override some filters, but it is not working correctly. From the quick look at the code I don’t think it is neccessary, as the get_posts(..) query used in that custom code uses a much different logic to filter the posts, which are then compared and filtered to the final results by the search.