Not receiving all Add to cart and Checkout Web-hooks

[Aayush92]

We have a custom APP developed for a Store and we have subscribed to cart/create and checkout/create webhooks but we are not receiving these webhooks every time a user creates a new cart or starts a checkout. 

While we are getting some webhooks, the unique cart tokens and checkout tokens are far from the numbers we see in-store conversion over time report in Shopify admin. 

We get webhooks with 10 unique cart tokens we see 100 add-to-cart sessions in the Shopify reports. What could be the reason for such discrepancy?