It's not uncommon to experience slower site speed after integrating Klaviyo with your WooCommerce platform. Many users have reported similar issues, particularly related to the size and loading speed of the JavaScript files associated with Klaviyo's features, such as signup forms. These scripts can add significant load time, especially if they are not optimized for performance.

The Klaviyo JavaScript files, especially those for embedded and popup signup forms, can contribute to longer load times. For instance, users have noted that certain Klaviyo scripts can take substantial time to load and may be blocking the main thread, which impacts overall site performance​

I have also noticed the teaser for the signup form is not automatic. It takes a few seconds for it to populate. 

Klaviyo review codes typically involve JavaScript that interacts with your WooCommerce site to collect and display review data. If the script isn't optimized for performance, it could potentially slow down page loading times.
 

Regard,

Yes, slower site speed after installing the Review Code on WooCommerce is a known issue for some users. It’s possible that the integration with Klaviyo’s new feature is causing some performance bottlenecks, especially if it's running additional scripts or data calls. You might want to try optimizing the code, reducing unnecessary scripts, or testing with caching plugins to help improve site speed.

You're not alone! Several users have reported experiencing slower site speeds on their WooCommerce stores after installing Klaviyo's Review Code, or other Klaviyo scripts. While Klaviyo states their JavaScript loads asynchronously to minimize impact, tools like Google PageSpeed Insights often flag it as a contributing factor to slower load times, especially on mobile. This can be due to the number and size of the JavaScript files loaded by Klaviyo, particularly for features like sign-up forms and review widgets. Some users have found temporary workarounds like delaying script execution or using caching plugins, but it's a known concern within the Klaviyo community.