i ve had that issue one day, that was a year ago
So i was fishing on my acc, and decided to check my offence history : i logged to see the offence list, and saw a appealable one, and decided to appeal : then i choosed the reason ''someone had acces to my account'', filled the text, and clicked ''appeal'' > then a warning appear saying something like ''if some one had acces to ur acc we re going to lock your account for safety reasons etc'', so i said ok, and clicked OK. then i go back to offence list , i see appeal pending..Now i go to my other window(in-game, fishing) and what i see : ''connection lost, waiting to restablish''
My guess on this : by making ur acc locked, jagex logs you out, and this is the only way to make someone logout.
but lol, offences needed