Thanks for the suggestion. It would be valuable to report "Unique abandoned carts" as a way to solve this problem.

I see the same problem with Matomo v3.9.1, plus:

I went to my site on a Samsung mobile device running the latest versions of Android and Chrome, opened a product page and added that item to the cart, then went to the Matomo dashboard -> Visitors -> Real-time in another browser window leaving the other window open on the store site), and there I saw my own visit logged and it showed up as an abandoned cart, which obviously isn't accurate since I was still on the same product page of the site, definitely had not navigated away from the site.

It's currently expected behaviour that when you add something to the cart, and don't purchase in the same visit, then it will count it as abandoned card. If you purchase in the same visit, the abandoned card will be gone.

I updated my previous comment to clarify that I did not leave the store site after adding an item to the cart, I left the window open on the store site (did not close it or navigate away) and opened a different window to check Matomo where I saw my session in the log indicating an abandoned cart even though I was still on the site in the other window. It seems that Matomo is assuming that any cart contents is abandoned until purchased, whereas ideally it would wait a certain amount of time (at least several hours) before considering the cart abandoned.

I realize that's not exactly simple to do, having already written software myself that sends email to a shopper when their cart has contents that has not been paid for after 24 hours. That's a bit simpler since that code runs on the store site. With Matomo being "remote" from the store, it'd need to be done different. Maybe by somehow flagging the session record as having cart contents, and then waiting some period of time (configurable in Matomo by the admin) before checking for records with that flag and updating them as being an "abandoned cart".

No need to clarify, I know what you meant. The current behaviour is kind of expected currently. We assume the cart is abandoned as soon as you add something to the cart unless you complete purchase in the same visit which then removes the abandoned cart again. At some point eg visitor log could check if visit_last_action_time is < visit_time and only show if more time has passed but otherwise there is likely not too much we can/will do here.