Can a development bundle be obsolete?

Can a development bundle be obsolete?

My Wordpress-site www.magoster.com gives a fatal error on a Contact Form7-Datepicker part in script-loader.php when customizing the theme (Twenty Seventeen, newly installed). I have no idea what causes this so I try to eliminate possible causes. As private person and not exactly an IT-expert I have some questions.

The development bundle I use is version 1.8.5. I have downloaded version 12.1 now. Is it possible that this old bundle can be obsolete and MIGHT cause errors?

If so, can I just FTP the 12.1 version files over the 1.8.5 development bundle files or are additional actions required.

Of course, I make a backup first  ;-)
Thanks for your advice!

Cheers
Rudolph Smits, Netherlands