This would be normal behaviour if you were holding down the Tilde key while creating the shapes (English version of Illustrator).
What happens if you quit and then restart Illustrator?
Nothing changes. The problem is still there.
What happens if you additionally quit and restart your computer?
Is it actually creating multiple shapes? Or if you deselect it and then re-select it and then manipulate the rectangle, does it act just like one shape?
My guess is that this is a previewing issue. Try toggling "Preview on CPU" in the "View" menu. You can also try toggling the "GPU Performance" option in the Settings dialog (ctrl/cmd + k) under the "Performance" tab.
As per the short video sequence it is rather obvious that it happens while creating the rectangles.
Normally, that is an intended behaviour (mass duplication) if you intentionally hold down the Tilde key (in other international versions of Illustrator the key may vary).
If that mass duplication happens without holding down the modifier key, most of the time it is a kind of temporary hiccup that can often be cured by just quitting and restarting Illustrator and/or quitting and restarting the entire machine.
In rare cases it may also be that the modifier key is stuck for some unknown reasons.
Rather unlikely that it is a GPU vs. CPU preview issue.
The problem was solved by restarting the computer twice.