Hello @Robb3n,
Welcome to the Klaviyo Community!
Was the integration made recently? If so, it may take some time for the historic data to be fully synced to Klaviyo. As detailed in the System Capacity for Historical Data Sync API Requests section of our Magento Integration System Requirements Help Center article:
When you activate the integration, Klaviyo automatically queues API requests to sync historical data including customer records, order records, and the product catalog. We attempt to do this quickly to empower marketers to use this data in their accounts as soon as possible. We also attempt to do this responsibly by limiting concurrency and by gracefully handling retries. If your store has a high volume of historical data, limited resource capacity, or other applications that make substantial API requests, we recommend consulting your Magento administrator to ensure your infrastructure is equipped to support the historical data sync. Your administrator may want to consider temporarily increasing resources, applying auto-scaling, or requesting that Klaviyo slow the requests
Depending on how much historic data the store has, it may take some time for the historic sync to complete and for your to see all of the data within Klaviyo. While a historic sync occurs, new activity that take place should still be recorded without interruption.
I hope this helps!
David