convert .odt or .docx to .html columns and textbox issue

Hi,
I have a document (.docx or .odt) with two columns which I convert to an html file using LibreOffice. The issue is that the columns disappear, showing all the text together.
Also, if I use a textbox, the conversion to html is not done properly: the box appears empty and the text out of the box.
I have tried with several versions of LibreOffice and I always have the same issue.