Blocking Error (Smoking gun errors): are visually obvious errors where a customer is evidently struggling during the customer journey. For example, you may see a customer clicking the “add to cart” button multiple times without allowing them to proceed.
Friction Error (Phantom errors): are conversion killers but there is nothing obvious that seems wrong in the video.The reason why you can’t visually see the impact of these phantom errors is because they usually are subtle elements of the user experience that cause friction. These errors on a large scale, however, can drastically impact revenue. If you want to see the impact of these errors, look at the Funnel Impact for the error and see the decrease in conversion. Therefore, even though you can’t see the full impact of these errors in videos, they still need to be solved because they are impacting your bottom line.
Here is an interesting read that talks about some of the impact of phantom errors and how their impact correlated to lost sales for Amazon: