I hope i understand what you mean, apologies if i do not completely.
This makes me think it's likely due to the PHP version of your website ( You refer to 'old wordpress site' ).
A websites PHP version can be updated within your Webhost's settings.
Note: The most recent PHP 8.0 has been known to cause a few issues until it becomes more widely used.
Hope that i have helped @User4000 & best wishes 🌝
Sincerely Richard
