uncoherent behavior in custom event to catch history log

Hello All,

I have created a custom event to send an email to users and inform them of the (log id) when a field is updated or deleted in customer screen.

Here is my custom event script : 

DECLARE
    log_lu_name_       VARCHAR2(1000);
    log_id_            NUMBER := 0;
    customer_id_       VARCHAR2(1000);

BEGIN

    --Set general parameters
    customer_id_ := '&OLD:CUSTOMER_ID' ;
    log_lu_name_ := 'CustomerInfo';


    BEGIN

    --Get log ID for history log search
    SELECT max(log_id) into log_id_
    FROM   history_log 
    WHERE  lu_name = log_lu_name_
    AND    keys like ('%'|| customer_id_||'%')
    AND    UPPER(history_type) IN ('UPDATE' , 'DELETE')  ;

    command_sys.Mail(sender_ => 'IFS Applications!',
                     from_ => '&USER_EMAIL',
                     to_list_ => '&USER_EMAIL',
                     cc_list_ => '',
                     bcc_list_ => '',
                     subject_ => 'customer : '|| customer_id_ ,
                     text_ =>'log_id_ = ' || log_id_,
                     attach_ => '',
                     rowkey_ => '',
                     mail_sender_ => '');

END;
END;

and the result of the mail in application message : 

When I run the query separatly in sql query tool , I get this result :

The number sent in the mail is always delayed by 1, I don’t understand where is the issue.

Can you please help me figure it out ? 

Thank you in advance,

Hanane