Update is breaking my site

Ever since I updated to version 4.9, my website has become extremely slow to load, sometimes not loading at all. When it does load, when I want to edit a post, there is this error message saying “Connection lost. Saving has been disabled until you’re reconnected.”

When I deactivate your plugin, these problems go away. I’m using the latest version of WordPress. I would like a copy of User Role Editor version 4.8 as that one had no issues with my site.

Please advise.

http://wordpress.org/plugins/user-role-editor/