Whole night? Greping every file? There are IDEs out there that can do the same task in 5 minutes wink. For example, Apache NetBeans 10 is a pretty good and have full PHP 7.3 support: https://netbeans.apache.org/download/nb100/nb100.html

I just imported UBB into my NetBeans installation and it shows immediately an error in cache_builders/calendar.php line 4:
Code
$output_text = "<table border="0"><tr><th>{$ubbt_lang['CALENDAR']}</th><tr><tr></td></tr></table>";
what should be:
Code
$output_text = "<table border=\"0\"><tr><th>{$ubbt_lang['CALENDAR']}</th><tr><tr></td></tr></table>";