If someone shares your internet connection they will be get as “same ip” on the game as you, also more than 3 alts should force this too.
Try to restart your internet machine and close and reopen your game browser/application…
Sometimes, just turn ON/OFF your own device/computer connection, also works…
NOTE: Turn on/off your device connection even fix faster the “heartbeat” bug than wait to the game to turn you really off when it comes to happen.
*HeartBeat: when you are kicked out of the game and try to log in, and they say “you are already logged in”