Yes, these kinds of transfer numbers are easily possible (even though other posters have said you don’t actually have 1,000 getting on or off at one stop). As an example, consider the subway of Toronto, Canada on its busiest line, Line 1. A subway train is 138m (450 ft) long with 6 cars (though there is no internal barrier between cars) and a capacity of about 1,500 people. Each car has 4 door sets per side, and these door sets are about 1.5m (5 ft) wide. People can easily fit through them in pairs, so moving 4 or more people per door set when in a rush is very doable. With 24 door sets (only one side opens at a station), that’s 96 people entering or exiting per second, so 10 or 11 seconds for 1,000 people. If you think 4 per second per door is too optimistic, then it’s 1,000 people in 20 seconds.

I’ve used self-checkouts in Canada and in The Netherlands. The ones here in Canada are just like the miserable experience you describe. Especially the weight sensor and the machine complaining. In The Netherlands I never had that issue (even with a second person helping me). I’m convinced companies have just turned the anti-theft settings up to aggravating false-positive levels over here.