Concrete falls and there are ghost blocks that you can go through but it looks like there is a block there. There is a screenshot of it.
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Thank you for your report!
However, this issue has been closed as Cannot Reproduce.
We were unable to reproduce the problem you are describing in the latest version.
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This relates to MCPE-22739 if not a dupe.
In general, the ghost block glitch can randomly happen whenever you make any changes to the terrain. Blocks you place may remain invisible, blocks you break may sit there until there are block updates nearby. The same happens when you /fill area but I think it's a similar but a different bug because the latter is nearly 100% reproducible while the former is <10%.