Nothing is saved in Account settings
In modules check for the hook_user_admin_settings_alter, check the form action and change it for the modules implementing those function

$form['#submit'][] = 'module_user_admin_settings_submit';

For reference sample forgot_username module

Instead of this 
$form['actions']['submit']['#submit'][] = 'forgot_username_user_admin_settings_submit';,

use this
$form['#submit'][] = 'forgot_username_user_admin_settings_submit';

In my case, forgot_username module breaks the account savings.

Reference : https://www.drupal.org/project/private_message/issues/2905184
Patch : https://www.drupal.org/files/issues/private_message-admin_settings_submit_handler_beta18-2905184-3.patch