Thanks for moving this to the WordPress forums :)
First to address the slowing down of the website. The plugin itself is only 800kb, and only adds a few hooks and actions to WordPress.
Now as for the issue of your site's clip buttons not working, here are some steps I would take to diagnose the issue.
- Please disable all plugins that you are running currently, leaving only WP Evernote Site Memory activated. Test the clipping button to see if it works. If it does, we know it is clashing with another plugin. Activate plugins one by one, and test the button after each one. When it stops working, we know that it is the plugin you last activated, and we can look at why that plugin might be breaking it. Deactivate that plugin, and continue to activate plugins one by one and see if another plugin breaks the button.
- If it does not work with all other plugins disabled, then it is an issue with your theme's code. Validate your code here and try to correct any errors you find.
Hope this helps, and let me know how you make out with this, especially step one, and then we can decide what to try next!