Mysql "ERROR 1045 (28000): Access denied" only when host is specified

I'm scratching my head with this issue. I have an Azure flexible for MySQL server with MySQL 5.7. I've created and give grants for a new user with the "%" wildcard, following the syntax (don't worry, I'm using fake names for everything):

MySQL [(none)]> CREATE USER 'mynewuser'@'%' IDENTIFIED BY 'password';
MySQL [(none)]> GRANT ALL PRIVILEGES ON *.* TO 'mynewuser'@'%';
MySQL [(none)]> FLUSH PRIVILEGES;

MySQL [(none)]> select user, host, account_locked from mysql.user where user = 'mynewuser'
    -> ;
+--------------+------+----------------+
| user         | host | account_locked |
+--------------+------+----------------+
| mynewuser    | %    | N              |
+--------------+------+----------------+
1 row in set (0.01 sec)

MySQL [(none)]> show grants for mynewuser
    -> ;
+------------------------------------------------------------+
| Grants for mynewuser@%                                     |
+------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'mynewuser'@'%'                      |
| GRANT ALL PRIVILEGES ON *.* TO 'mynewuser'@'%'             |
+------------------------------------------------------------+

But when I try a connection from a remote machine, if I try to specify the host (even localhost), I've got an Access Denied error from 172.26.3.34 (The remote machine, JUMPSRV01 ip):

JUMPSRV01> mysql -hSRVDB01.mysql.database.azure.com --ssl=true -umynewuser@SRVDB01 -p 
Enter password: 
ERROR 1045 (28000): Access denied for user 'mynewuser@localhost'@'172.26.3.34' (using password: YES)

JUMPSRV01> mysql -hSRVDB01.mysql.database.azure.com --ssl=true -umynewuser@localhost -p 
Enter password: 
ERROR 1045 (28000): Access denied for user 'mynewuser@localhost'@'172.26.3.34' (using password: YES)

JUMPSRV01> mysql -hSRVDB01.mysql.database.azure.com --ssl=true -umynewuser@JUMPSRV01 -p 
Enter password: 
ERROR 1045 (28000): Access denied for user 'mynewuser@localhost'@'172.26.3.34' (using password: YES)

**However**, if I don't specify the host in the username parameter, it works

JUMPSRV01> mysql -hSRVDB01.mysql.database.azure.com --ssl=true -umynewuser -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 117
Server version: 5.7.44-azure-log MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MySQL [(none)]>

What am I missing? The problem i am facing is that I'm replicating a database, and all the services and clients connects using the "username@dbhost" syntax and I don't know how many host or services are trying to connect to the database like that, so modify the clients and services connection string is no possible.