Hi, I fixed this problem on my sites.
Because preg_replace deprecated since php 5.4. We can use preg_replace_callback instead of.
Change this code in seo-auto-link.php line 76 and 253
$text = preg_replace('%(<h.*?>)(.*?)(</h.*?>)%sie', "'\\1'.SEOAutoInSpecChar('\\2').'\\3'", $text);
to
$text = preg_replace_callback( '%(<h.*?>)(.*?)(</h.*?>)%si',
function ($m) {
return stripslashes($this->$m[1]) . SEOAutoInSpecChar( stripslashes($this->$m[2]) ) .stripslashes($this->$m[2]);
},$text);
But I’m not sure this working 100%. Wating update from plugins.