The problem firstly occurred a few days after open the realm for the first time and it couldn't be solved by the support, FAQ's an  or other methods. The problem is that you loose the connection to the server every 30 minutes. It is not possible to rejoin directly because it lasts at least about 5 minutes until you are able to rejoin. As I said it happens every 30 minutes. If you are back on the server you can see that your progress of the 30 minutes was reset. Opening and closing the realm doesn't work and resetting and uploading the world again as well.