Great! You were right. After testing I've found that fail2ban fails when its configuration is changed. Thank you for your patience.
However, according to the documentation showed in jails.conf file, it's necessary to modify some configuration parameters for some filters, such as the dbpurgeage variable for the recidive filter. Then the question should change...
Is it possible to change the fail2ban configuration without breaking the program? I understand that the answer must be yes when some essential parameters are touched. In my case I only wanted to modify the dbpurgeage variable for the reason explained above. Is it allowed to modify some parameters without affecting the program?
Thanks!