I get this a lot as well on Race v1.1.1 (and don't tell me 8Mbit/s is a bad internet connection, or that 40 ms ping is high!).
Usually the first visual clue of being disconnected from the server is when a checkpoint won't "check" when I drive through it. Sometimes I can still see other people driving, sometimes not, but most of the time people just get stuck in whatever they were doing (like someone executing a left turn will just drive in circles). Most of the time I will soon be disconnected from the server with a message ala "Client not responding", but not all of the time - sometimes the "checkpoint doesn't check" will be the ONLY clue of being out of sync/connection with the server (ie I can still drive and so can others, only when I touch a checkpoint nothing happens).
This bug can get quite annoying, especially when you are leading a race and suddenly a checkpoint won't check and you have to reconnect, consequently loosing the entire race.
BTW, why doesn't MTA have a console command to (quickly) reconnect to a server? I have to type: "disconnect" every time, then get to Quick Connect from the menu just to reconnect to a server... (thank God I always connect to a server using Quick Connect anyway, otherwise I'd probably have to find the correct server in the browser every time!)