My friends are stuck at building terrain at realms

Hello!

I host a minecraft realms and I invited my friends to play on it. For the time being they we're exploring the map and they could see a chunk load, they are so far away from the spawn and they decided to reconnect but once they reconnected they are stuck with the building terrain loading. 

 

Can anyone give any advice or knows how to resolve this? thank you so much for the answers and help.