Transcribe .docx files via python-docx to modify font and font size. Need to reconstruct paragraphs in target files
This modification resolves this issue.
Thanks to Scanny at Stack Overflow

for src_paragraph in src_doc.paragraphs:
            tgt_paragraph = tgt_doc.add_paragraph()
            for src_run in src_paragraph.runs:
                print('Run: ', src_run.text)
                tgt_run = tgt_paragraph.add_run(src_run.text)
                if src_run.bold:
                    tgt_run.bold = True
                if src_run.italic:
                    tgt_run.italic = True
                if src_run.underline:
                    tgt_run.underline = True