Symptoms
You may have gone through everything to find out why a cPanel user and password is unable to access phpMyAdmin and even reset the cPanel users password but no matter what is done access is denied.
Workaround
If the user has a .my.cnf file in the users home directory with settings like this
[root@server /home/cpaneluser]# cat ./.my.cnf
[client]
password=somepassword
user=cpaneluser
[root@server /home/cpaneluser]#
and the password isn't the currently cPanel users password access will be denied. Either move this file
mv -v /home/cpaneluser/.my.cnf{,.old}
or update the users .my.cnf file with the new password.
If you move aside the .my.cnf file, you may need to reset the user's cPanel password in order to sync it with the MySQL user's password.
Please note that cPanel doesn't add these files nor does our software update these files automatically leaving passwords in clear text.