The Joomla function ContentHelperRoute::getArticleRoute is used in AcyMailing for the subscription module and the article insertion tag.
It has always been loaded by default, but maybe something has recently changed. If this is the case, we may need to modify our extension to make it work with every template.
Could you contact our support, ask for Jeremy and either send a download link for the template you're using or send an access to a testing site where the issue occurs? I'll post here the solution once found.