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?