I have a theme that uses several template files like `page.html.twig`, `page--title.html.twig`, etc. 

I installed Metatag to make my website more understandable when sharing links to it via LinkedIn. However, after installing the Metatag module, my <title> tags in all pages except admin are blank. I also tried to specify the title tag's content within Metatag as `[current-page:title] | [site:name]`, but the title tag is still empty

I know this is a common issue. I have found this online 

> When using custom page template files, e.g., page--front.tpl.php, it
> is important to ensure that the following code is present in the
> template file: `<?php render($page['content']); ?>` or `<?php render($page['content']['metatags']); ?>`. Without one of these
> being present the meta tags will not be displayed.

However, that looks like an advice for Drupal 7 only - and I don't know how to do this in a TWIG file used by Drupal 8. Any advice would be appreciated.

EDIT: My TWIG files are as follows:

 - page.html.twig: https://codeshare.io/5ezppb
 - html.html.twig: https://codeshare.io/2KWnnE
 - page-title.html.twig: https://codeshare.io/G8XeeD