Inconsistent Markdown Output with generate_multimodal_pages Method in Docling

### Bug
I’ve encountered a recurring issue with the Docling library where the Markdown output generated from PDF documents is inconsistent. Specifically, when using the `generate_multimodal_pages` method, I frequently find that content is randomly lost in the `content_md` column. This has happened with multiple PDF files, leading to incomplete and poorly structured Markdown outputs, especially for tables and complex layouts. The lost content is usually found in the `ocr_content` column.

### Steps to reproduce
1. Use the following code to convert a PDF document directly to Markdown:

```python
source = "https://arxiv.org/pdf/2408.09869" # document per local path or URL
converter = DocumentConverter()
result = converter.convert(source)
print(result.document.export_to_markdown())
```

This method produces a complete and well-structured Markdown representation of the PDF.

2. Use the following code to generate Markdown page by page:

```python
import pandas as pd
import datetime
from pathlib import Path

def main():
logging.basicConfig(level=logging.INFO)

input_doc_path = Path("./tests/data/pdf/2206.01062.pdf")
output_dir = Path("scratch")

pipeline_options = PdfPipelineOptions()
pipeline_options.images_scale = IMAGE_RESOLUTION_SCALE
pipeline_options.generate_page_images = True

doc_converter = DocumentConverter(
format_options={
InputFormat.PDF: PdfFormatOption(pipeline_options=pipeline_options)
}
)

conv_res = doc_converter.convert(input_doc_path)

output_dir.mkdir(parents=True, exist_ok=True)

rows = []
for (
content_text,
content_md,
content_dt,
page_cells,
page_segments,
page,
) in generate_multimodal_pages(conv_res):
dpi = page._default_image_scale * 72

rows.append(
{
"document": conv_res.input.file.name,
"hash": conv_res.input.document_hash,
"page_hash": create_hash(
conv_res.input.document_hash + ":" + str(page.page_no - 1)
),
"image": {
"width": page.image.width,
"height": page.image.height,
"bytes": page.image.tobytes(),
},
"cells": page_cells,
"contents": content_text,
"contents_md": content_md,
"contents_dt": content_dt,
"segments": page_segments,
"extra": {
"page_num": page.page_no + 1,
"width_in_points": page.size.width,
"height_in_points": page.size.height,
"dpi": dpi,
},
}
)

# Generate one Excel file from all documents
df_result = pd.json_normalize(rows)
now = datetime.datetime.now()
output_filename = output_dir / f"multimodal_{now:%Y-%m-%d_%H%M%S}.xlsx"
df_result.to_excel(output_filename, index=False)
```

3. Compare the `content_md` column with the output of the original Markdown; you should see that they don't match.
4. The issue is more prevalent with PDFs that contain many tables.

### Python version
3.12