Broke my world

[Majjon]

imported a few maps with the "generate structure" feature, opened my world and it is unrecognizable. massive chunks of the world are completely missing and my build I've spent months on is ruined. Even the world's file size has lost over 100mb. Lucky i made a backup :)
playing on Bedrock version 1.20.41 (windows 10)
hope this issue gets fixed because it would be devastating to lose a massive project like this one.
Maps came though just fine though.

what remains of my 64x72x64 underground cathedral that i built in survival is visible but that's all that's left. SO glad i made a backup this morning

[tryashtar]

Hey, thanks for the info. I'd certainly like to prevent this if possible. If I can replicate it consistently, I can fix it.
Do you think it happens every time with your world? If so, I'd much appreciate if you could upload your backup so I can test