I was able to reproduce an issue with your document.
The problem occurs because the Paragraph element’s formatting is changed, more specifically the Paragraph.CharacterFormatForParagraphMark.
In short, some information is lost because the previous Cells[0].Blocks[0] element is replaced with a new Paragraph element which has a default formatting.
We could keep or resolve that character formatting information (the font size, font name, etc.), but note that you will still end up losing the paragraph formatting (the 2pt spacing after and before, the single line spacing, etc.).
Because of that, I believe your current approach (using table.Rows[1].Cells[0].Blocks[0].Content.LoadText) is better.
The only thing I would suggest you is to first check that there is one block in the TableCell.