IF you are using any third party plugins related to login then please try deactivating it.
If your site is on wp-engine then please refer :
https://wplms.io/support/knowledge-base/fixing-login-widget-on-wplms-sites-hosted-on-wpengine-com/
If you have a different url to login then please also try using this code (paste it in your wplms-customizer.php file in wplms customizer plugin) :
add_action('wplms_login_widget_action','my_custom_login');
function
my_custom_login($link){
return 'http://yoursite.com/login_url';
}
cahnge this : " http://yoursite.com/login_url " to your custom login url .