1.13.1 was just released so I ran over to my realm and was greeted with covered with diamonds. I was like what I already had this and when I opened my advancements I saw that they were all gone except for that one witch I just acquired.
REALMS-1276
Opening a 1.13 World in 1.13.1 Resets Advancement & Most Statistics
Resolved
Cannot Reproduce
1
Never mind. After more testing it turns out that it was just a corruption in the Minecraft realms world download/backup. Instead, you should probably fix your Minecraft realms 🙂