Why is Drupal not launching the site?

Question

Drupal

Didn't do anything and suddenly the site stopped working, Drupal 8.4
Cannot use object of type Drupal\filter\Render\FilteredMarkup as array in Drupal\Component\Utility\Unicode::substr() (line 451 of core/lib/Drupal/Component /Utility/Unicode.php).
The lines there are:

// Find the ending byte offset.
      if ($length === NULL) {
        $iend = $strlen;
      }
      elseif ($length > 0) {
        // Count all the characters except continuation bytes from the starting
        // index until we have found $length characters or reached the end of
        // the string, then backtrace one byte.
        $iend = $istart - 1;
        $chars = -1;
        $last_real = FALSE;
        while ($iend < $strlen - 1 && $chars < $length) {
          $iend++;
         $c = ord($text[$iend]);   // Ругается вот на эту строки
          $last_real = FALSE;
          if ($c < 0x80 || $c >= 0xC0) {
            $chars++;
            $last_real = TRUE;
          }
        }