We have tested your issue with the latest version: Aspose.Cells for Java v16.11.8 with your provided sample code and observed the issue. The text style of cells A24 and A25 etc. is changed when saved to Html.
We have logged this issue in our database for investigation. We will look into it and fix this issue. Once the issue is resolved or we have some other update for you, we will let you know asap.
This issue has been logged as
CELLSJAVA-42091 - Text style of some cells is wrong when saved to Html