init_connect not executing

Question

From this question I was able to make my init_connect = "CALL mydb.Warnings()", but a user login in does not triggers the SP.

the SP is like:

CREATE DEFINER=`root`@`localhost` PROCEDURE `Warnings`()
BEGIN
select * from mydb.log;
END

The user 'Tk3' is able to call the SP with success, but it ain't allowed to do Selects.
I did check with show global variables like 'init_%'; and the correct value is set.
I'm missing the reason for this failure, could you help?

1st Edit:
After the @danblack and @Rick-James suggestions I altered the SECURITY to:
CREATE DEFINER='tk3'@'localhost' PROCEDURE 'warnings'()
but the behavior is the same.
:( I'm lost ):

2nd Edit:

    MariaDB [(none)]> show create procedure logdatabase.warnings;
    +-----------+--------------------------------------------+----------------------+
    | Procedure | sql_mode    
    |Create Procedure  
    |character_set_client | collation_connection | Database Collation |
    +-----------+--------------------------------------------+----------------------+
    | warnings  | NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |

    CREATE DEFINER=`tk3`@`localhost` PROCEDURE `warnings`()
    BEGIN

    SELECT * FROM logdatabase.log_activity;
    END 
    | utf8                 | utf8_general_ci      | latin1_swedish_ci  |
    +-----------+--------------------------------------------+----------------------+
    1 row in set (0.00 sec)

MariaDB [(none)]> show grants for 'tk3'@'localhost';
+------------------------------------------------------------------------------+
| Grants for tk3@localhost                                                     |                           
+------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'tk3'@'localhost'                                      |   
| GRANT SELECT, CREATE, EXECUTE, CREATE ROUTINE, ALTER ROUTINE ON `logdatabase`.* TO 'tk3'@'localhost' |
+------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

I'm not showing the SHOW CREATE USER because it's returning an error:

MariaDB [(none)]> CREATE USER 'mytest'@'localhost';
Query OK, 0 rows affected (0.01 sec)

MariaDB [(none)]> show CREATE USER 'mytest'@'localhost';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'USER 'mytest'@'localhost'' at line 1

(this print was made with 'root' - I will deal with this strange thing later)