Failed to replace a new world into one of my realm world slots

Yesterday, I have some issues with my realm. So, if I replace my current realm world with a new one, the system would say that the world has been replaced successfully, but when I try to join the realm, it won't work. Then, if I want to switch to another slot, to activate another one. It keeps giving me failed to retrieve realm information.  I just can't put my desired world into the realm.