Logging in to a realm error

When i try to login to a realm(i dont own it) it allows me to play for a couple of seconds and then it gives the error:''Internal Exception: java.net.SocketException: Connection reset''. i dont understand this because my internet is good and my cpu is not at 100%. i looked on the internet and nothing has worked. 

sometimes i can play for hours at a time and sometimes i cant only join for a couple of seconds.