There is a missing portion of the world that doesn't load, as if it's corrupted. Unsure of what to do. 

Backing up the realm and trying to play locally I just get kicked anytime I try to walk near the area that won't load and get the message "You are out of data storage space and Minecraft is unable to save your progress! Minecraft will return you to the Main Menu to clear up storage." 

This is a server with close friends and my little brother on here, I'm afraid it's corrupt and eventually, this will break the game and I won't really know what to say or do to my little brother who's worked so hard in his first survival. Any ideas on how to fix this land that won't load without losing the entire realm?

This is a realm I started by just clicking the free trial about a month ago, so it is one generated as a 1.12 realm from the get-go. Screenshots of the missing land below