Why did WordPress 4.5 break my website?
WordPress’s Core will automatically update your website to the latest WordPress version when the newest version has been tested and deemed safe for release, unless you have preventative measures already in place. Wordpress 4.5 included many new updates and changes which can all be seen here: https://codex.wordpress.org/Version_4.5
There are other problems we have seen that broke other users websites but for the most part it usually had something to do with the jQuery update.
How can I fix this?
There are a few solutions to fix this issue but you most likely should have a development team to help you.
The best solution would be to update the core to 4.5, then update all the plugins, and update the theme (always make a backup of the files and database before you do this). Usually if you have all the latest plugin’s and the latest theme files implemented on your site any broken area’s should be corrected.
Another solution would be to replace the new jQuery library with the last version. This is not the best idea because once another WordPress version is updated on your site it will overwrite the older library. Use these files here and replace the current folder located here: wp-includes/js/jquery.
How can I prevent this in the future?
The best way to prevent WordPress 4.5 or any newer version from breaking your website in the future is to have one of our WordPress Maintenance & Care Plans. We not only make sure your website is updated to the newest versions of WordPress, plugins and themes, but we also go in on a daily basis and actively watch your site(s) for security and malicious activity, create daily backup’s, clean up spam, database overhead, monitor website uptime, and more.
You can always set your wp-config file so your site does not automatically update. You can find more information about how to implement that here: https://codex.wordpress.org/Configuring_Automatic_Background_Updates. This way you can have time to test the new version and make sure it works with your website before pushing these updates LIVE.