kundanmore on "Upgraded to WP 4.5 and now my site is broken"

Please note that those of you having issues are only a few (and a rare few at that - likely well under 1%) of the millions of WordPress installs with the 4.5 update. The majority of installations have worked fine.

WordPress is tested fairly well across a wide variety of servers and setups - in fact you can help with testing by participating in WordPress betas (https://wordpress.org/plugins/wordpress-beta-tester/). I also recommend that you have a development/testing/staging server to test plugins, themes, and WordPress core updates against prior to implementing it on a production server.

For those of you having issues the most likely culprits are plugins or themes that have not been tested and/or updated to work with 4.5.

To find out what's causing the issues, please disable all plugins and use a default theme and see if everything works. If not, do a manual upgrade (see https://codex.wordpress.org/Updating_WordPress#Manual_Update).

Once you have a "out of the can" WordPress site (no plugins enabled and a default theme), tu on your non-default theme and see what happens. If there's issues, contact the theme developer for support or updates.

If everything works with the theme, move on to plugins. Enable one of your plugins and test. Does everything work? Good, move on to the next plugin and enable it. Then test. Do this until you have enabled all the plugins or until you've identified issues. If there's an issue, note which plugin you last enabled and then contact the plugin developer for further support or updates.