[Koha] search patron not working

Hi, I am using Koha 22.05.00.000 on Ubuntu 18.04.6 LTS. Since a few (Koha) updates ago, I've noticed that the "search patrons" function is not working. I type in the first letters or the full name of an (existing) patron, the search engine starts, but no one is found. In order to display the patron's details, I have to look for an item he/she certainly has borrowed, and click on the patron's link in item's "Status" tab. Any hint? Many thanks and best regards, Giuseppe.