I downloaded 1.13 on my pc and when I tried to open my  "creative mode" world, I got a screen asking "This world was last played in version 1.12.2; you are on snapshot 1.13. Please make a backup in case you experience world corruptions." So I clicked "Backup and load" and when the world loaded, I had all the same items in my inventory but all my creations are gone and instead there are new ice blocks and things in the place of my creations . 

https://paste.ubuntu.com/p/twZzQ9Nkyh/ 

Also, I tried running 1.12 and created a test world to see if it works in 1.13 and it did work. But my original creative mode world is blank.