After updating to 1.13 anyone attempting to log on to my realm receives an error message. Mine tells me to use load a back-up and anything after the 1.13 update results in the same error. I also can't roll back my version of Minecraft to 1.12.1 so everytime I log on it updates the Realm. Loading a back-up seems to have fixed the problem (for the last 15 minutes at least).