I joined my friends world that has always been survival and was generated on Minecraft: Xbox One Edition and last night he converted the world to the bedrock code base. After joining I equipped my elytra and attempted to take off with rockets and within seconds he reported his game had crashed. My game continued to run until I experienced the disconnected dirt screen.

We were able to reproduce this 6 times all with the same steps.

1. Join converted survival world
2. Put on elytra
3. Try fly with rockets
4. Host game crashes.

Note: we had not tried this on a realm as we could not get this specific world to upload correctly (will file separate issue for this if one does not exist)