Problem with child theme after change in article_details.tpl

I am creating a grandchild from Classic Theme and I noticed that recently it has been a change in the Classic Theme: Support for HTML formatting in titles & reduce use of getCurrentPubli… · pkp/classic@f11e335 · GitHub.

This change seems to give a problem with my grandchild theme in which I have to copy the “article_summary.tpl”. So instead

if (!$section.hideAuthor && $article->getHideAuthor() == $smarty.const.AUTHOR_TOC_DEFAULT) || $article->getHideAuthor() == $smarty.const.AUTHOR_TOC_SHOW}

there is

{if (!$section.hideAuthor && $publication->getData('hideAuthor') == \APP\submission\Submission::AUTHOR_TOC_DEFAULT) || $publication->getData('hideAuthor') == \APP\submission\Submission::AUTHOR_TOC_SHOW} (and similar).

If I use the new version of the .tpl I get this error:

PHP Fatal error: Uncaught Error: Class "APP\\submission\\Submission" not found

I can copy and past the previous version of my child theme, but I wonder why I get this error and if it a matter of an older version of OJS: I have OJS version.