Bedrock conversion into deepslate tends to sometimes fail while upgrading worlds created in the pre-bedrock codebase. In the images shown I opened the world both in the bedrock codebase and in the java edition. In the bedrock codebase, it is showing the bedrock conversion failing to convert all the bedrock on y5, while on the java edition in the same location it's shown to have converted all the bedrock into deepslate.

This can also be seen as a relation to MCPE-147373 where deepslate is failing to generate this high.
I couldn't attach the world files on here so I'll link them here in dropbox.