If your site is completely messed up or just a feature or two are off after upgrading/updating the solution is usually as simple as turning the feature off and back on, re-saving settings, changing the page template, saving and then back again and saving etc to work the kinks out. Last resort would be to Restore Defaults.
Another very important step is to disable ALL third-party plugins and see if this resolves your issue. If it does, re-enable them one at a time until you find the one causing the problem. If it’s an essential plugin, please make a post and report the plugin that is causing the conflict and we will see if it is our problem or the plugin.
Naturally, as the design evolves this may “undo” or break some of your Custom CSS that I’ll be here to help with.
It’s important to note that upgrading is optional and should always be done with caution and understanding.