They are registering for each day's logon,
You can manually add the following lines to your log.csv,
;18/05/2017 10:00:00;ocsweb;CONNEXION;USER:admin;192.168.0.34;
admin;18/05/2017 10:00:00;ocsweb;PAGE;;192.168.0.34;
;18/05/2017 10:00:00;ocsweb;CONNEXION;USER:admin;192.168.0.34;
admin;18/05/2017 10:00:00;ocsweb;PAGE;;192.168.0.34;
To simulate previous days, with past dates
And your graph will look better.