Please check with below steps.

Option 1: Your may need to look into the Events Manager details.

In the list of facebook Events Manager, the number of Total events is the sum total of the two methods of Browser and Conversions API.

You can click "View details" to view the details, which shows how much data is returned by each of the two return methods.

Option2: You have installed your pixel multiple times

In this case, please make sure you only install once.

1.shopify-Customer events

2.Shopify-Apps and sales channels-facebook&Instagram-Settings-Behavior will be tracked with this pixel