Game on Realms cannot be continued

I am playing Minecraft on Realms server.

Now I am encountering the problem that the connection will be disconnected as soon as  I spawn to my world.

My world map size is 456.42 MB now.

Connection of my device (iOS) to Realms-server looks  OK. Because my another small world on Realms is working fine. 

please can you confirm if there is something wrong.