Error 500 in Submission

OJS 3.1.2.1
Good morning. When I try to click on the title of an already entered submission I get error 500. Looking in the error logs I find this:
PHP Fatal error: Uncaught → Smarty Compiler: Syntax error in template “app:app:layoutsbackend.tpl” on line 15 “{title|strip_tags value=$pageTitle}” unknown tag ‘title’ ← \n thrown in /var/www/clients/—/—/web/lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_templatecompilerbase.php on line 15’, referer: Login | AGATHÓN | International Journal of Architecture, Art and Design

How can I solve this problem? Thank you