When I sync a world from the old console edition, an aproximadetely chunk size of the world is severely affected. This happens around the original spawn point on the seed, and all of the blocks around it are changed into an old version of the chunk from that world.
Thank you for your report!
We're actually already tracking this issue at MCPE-58480, so we will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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