This issue is the similar issue which is reported here https://github.com/sysown/proxysql/issues/1538.
I found some workaround to fix this issue, without initialising or recreate/reconfigure your ProxySQL node.
We have default ProxySQL user “admin” to connect the ProxySQL over the 6032 port.
Once we connected and created the “admin” user account inside the mysql_users table and then loaded into the memory and persisted to disk, we are unable to connect the ProxySQL over port 6032 anymore.
ERROR 1045 (28000): ProxySQL Error: Access denied for user 'admin'@'' (using password: YES)
To fix this issue, we can login to backend via sqlite3 and remove the “admin” user from mysql_users tables.
cd /var/lib/proxysql/ sqlite3 proxysql.db sqlite> SELECT * FROM mysql_users; sqlite> DELETE from mysql_users where username='admin';
Then restart the ProxySQL service.
service proxysql restart
Tip : Never create admin user account (admin_credentials) inside the mysql_users table which is mentioned in the ProxySQL documentation as well. https://github.com/sysown/proxysql/wiki/Global-variables#admin-admin_credentials [users in admin-admin_credentials cannot be used also in mysql_users table.]