Why are there missing sessions in GA shopping behavior analysis?

Question

When I check the shopping behaviour analysis in Google Analytics, I do not understand why there is a decent number of sessions missing.

According to Google's support page:

The Shopping Behavior Analysis report lets you see the number of sessions that included each stage of your purchase funnel, how many sessions continued from one step to the next, and how many abandoned the funnel at each stage.

But even at their screenshot you see that there are sessions missing:

12,067,900 - 7,682,634 != 4,117,342 ... so what happened to this 267,924 sessions?

Answer 1

The answer is quite easy when you look closer to the screenshot or your Google Analytics account. The missing sessions enter the funnel in later steps - like you can see in the screenshot.

If you hover over the small bar at "Sessions with Add to Cart", you'll see a number close to 267,000.

In your shop this can occur when your visitor fulfils one or two steps of your funnel, then goes AFK for 30 minutes or more (you can setup this timer at Google Analytics) and then continues his shopping. A new session starts when he comes back after old session run out.