Hello @jannikkay,
Welcome to the Klaviyo Community!
By default, Shopify wouldn’t actually sync an add to cart event to Klaviyo. For this reason, in order to record an add to cart event, the instructions found in our How to create an "Added to Cart" event for Shopify Help Center article explains how to install a custom add to cart event which is triggered whenever someone is cookied clicks on the add to cart button to be synced to Klaviyo.
Oftentimes, custom events need to be manually connected to Klaviyo. The add to cart event is not different - including this addition mysterious add to cart event that is triggering. I would suggest double checking on other third-party tools and/or apps you’re using on your site that may have a connection to Klaviyo which is triggering this event.
In small instances, I have also seen times where users may have installed the add to cart code incorrectly which may have some issues such as a duplicate event firing. However, all of which goes back to reviewing how your site is setup and coded. If you need more hands on assistance, I would suggest consulting with your own developer who can better review your site for any inaccuracies. If you need an introduction to a developer, we have a vast network of Klaviyo Partners who specialize in such areas.
I hope this helps!
David