Maybe this is not the answer you look for but giving one of below a try could maybe help you out?!
Ofcourse you have FTP or SSL access.
If you don’t have one of them, don’t bother to read any further!
The good old make a backup from in this case
functions.phpbefore you start adding/editing is wishdom and could be important.
Start by activating debug in wp-config.php to see(hopefully) possible errors when some seems to bother WordPress.
Option 1:
Add in functions.php the following code snippet when your admin user has ID number 1(ONE):
/**
* Read more {@link https://codex.wordpress.org/Function_Reference/wp_set_password}
*/
$user_id = 1;
$password = 'newpasswd';
wp_set_password( $password, $user_id );
Please note: This code should be deleted after ONE page load, otherwise the password will be reset on every subsequent load, sending the user back to the login screen each time.
Change both to your preference! When the Administrator is not having user_id 1 and you have no idea which user_id number it should be, please forget this option. (no need to tryout!)
When you have add the snippet try to login your site. (be sure browser cache is empty)
Try now to login with your admin name and your new created password.
Successful? If yes, delete the snippet from functions.php and all should be fine now.
Not successful? Delete the snippet and try option 2.
Option 2:
Add in functions.php the following function, which will*(should)* create a new administrator user for you. Change $username \ $email \ $password to your preference. (a correct working email address would be logical)
/**
* Create a new user with admin caps
*
* Read more {@link https://codex.wordpress.org/Function_Reference/wp_create_user}
*
* @version WP 4.7.3
*/
add_action( 'init', 'wpse262478_add_new_adminuser' );
function wpse262478_add_new_adminuser()
{
$username="aname";
$email="[email protected]";
$password = 'LZTf$f$FR)Y@xye';
$user_id = username_exists( $username );
if ( !$user_id && email_exists( $email ) == false )
{
$user_id = wp_create_user( $username, $password, $email );
if( !is_wp_error( $user_id ) )
{
$user = get_user_by( 'id', $user_id );
$user->set_role( 'administrator' );
}
}
} // end function
(make sure the browser cache is empty, which can always be helpful in these situations)
If you are successful you can login with the new created admin account (if not directly working press F5 on the keyboard to refresh a few times) and can delete the function from your functions.php. If you are not having success you still have to delete the function because this option seems also fruitless.
Hopefully one of the above did help, if so, stop reading and take a deep breath. If not, maybe followng could be helpful.
As you already tried accessing through phpMyAdmin (seen the chat discussion) which was also fruitless, you can still try another option which is not always helping but at least you did a -try and error-.
Option 3:
Rename your plugins folder to something else and retry option 1 or 2.
If successful, login, rename the plugin folder back to plugins. Now you have to enable 1 by 1 each plugin and check if all still is working.
When all seems okay then at least you found a solution but still have no answer about the ‘why was it not working’ but it would be too far to digg into that issue but at least now you can take some time to find out what it maybe could be.
ps, did you check your functions.php also, maybe there is code which could be the culprit for this dilemma?!