First, I would like to thank you for the solution that solved my problem.
Now there are similar problems when I try to edit a record:
Warning: PDO::query(): SQLSTATE: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ', rank.subject_id, title_id, so.source_id, rank_id, description_override, subjec' at line 1 in C:\wamp64\www\sp\lib\SubjectsPlus\Control\Querier.php on line 89
I guess that I should change the queries somewhere in the code again.
I also tried with MySQL version 5.7 but I have problems starting the service.