@rgosse75 I have tested the plugin in wordpress 4.8, it is working fine for admin as well as frontend user login.
Please follow these two methods to debug this.
Method-1)
Deactivate the plugin, and then copy the following snippet in your theme functions.php file.
add_action('wp_login', 'save_user_login');
function save_user_login($user_login, $user) {
echo "debug start";
echo "<br>";
global $wpdb;
echo "<pre>";
print_r($user_login);
echo "<br>";
print_r($user);
echo "<br>";
echo "debug end";
}
Now re-login as admin.
Now activate the plugin and re-login as admin.
Share the two outputs with us.
Method-2
The following function is responsible to save user login data from frontend as well as backend:
wp-content\plugins\user-login-history\admin\class-user-login-history-user-tracker.php
function is “save_user_login”
You should debug this function.