Hello,
The OOXML standard (DOCX documents) requires that all cells must have at least one content (this can be a paragraph, other table, a blank space...), otherwise, MS Word shows a corrupted DOCX.
You can't hide/remove all cell contents. At least one content must be added to the cell. If you set display: none to all cell content when importing HTML then no content is added to the cell, and at least one content needs to be added.
Regards.