Fatal error: Uncaught Error: Call to a member function is_rtl()

Hello,

We have e-Newsletter plugin installed on our site, when we try to create new newsletter or edit existing on customize page we see error. We have latest version of plugin and WP, also we tried to downgrade the plugin version as on another site we have it up and working fine.

Fatal error: Uncaught Error: Call to a member function is_rtl() on null in /var/www/wordpress/wp-includes/script-loader.php:986

We have tried to debug this issue on our site by switch to default WP theme and also by disable plugins, but still no luck. Could you please guide us what the issue could be so we can solve it and use the plugin.

Here is screenshot:

Thanks.