Sounds like you converted it before they added world blending which would explain why it all happends, if you still have a backup of the old 1.14 world you can try to convert it in the pre release
@Moesh I tried to select Feature but could only select bug
Same to me on my windows 10 laptop it laggs a lot and just chrashes
Sounds like you converted it before they added world blending which would explain why it all happends, if you still have a backup of the old 1.14 world you can try to convert it in the pre release