The first thing come into my mind Is to check if there Is some http CSS that Is not be loaded when you have the secured connection… Just check It from browser
Alright, it was actually a simple fix. Just my ignorance in working with Wordpress. I’m much better with Drupal.
Under ‘Settings > General’ there’s a site URL, that was set to the truenas container’s address by default. Changed it to the address I’m serving with NPM and now all is well.