The scroll wheel shows before the pop-up initiates because the app is querying the BigCommerce API to see what is in the customer’s cart.
It doesn’t happen often, but there’s the potential for latency from the BigCommerce API which could cause the pop-up to take longer to initiate. The scroll wheel shows so the customer isn’t surprised by a pop-up after a few seconds if there is latency.
To Disable...
Pop-up Behavior > Show loading wheel before pop-up displays.