Unprecedented KeyError occuring

### Bug

I was using docling to convert pdf file, and noticed KeyError originating from docling from the line
doc = converter.convert(pdf_path)
the pdf path contains the pdf file.
The error is occurring for same pdf but with different numbers on KeyError.
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### Steps to reproduce

Unfortunately cant share the same pdf.
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### Docling version

Docling version: 2.58.0
Docling Core version: 2.49.0
Docling IBM Models version: 3.10.1
Docling Parse version: 4.7.0
Python: cpython-312 (3.12.3)
Platform: Linux-6.14.0-1012-aws-x86_64-with-glibc2.39
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### Python version
File "home/src/extractors/pdf_markdown.py", line 79, in process_single_page
doc = converter.convert(pdf_path)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/pydantic/_internal/_validate_call.py", line 39, in wrapper_function
return wrapper(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/pydantic/_internal/_validate_call.py", line 136, in __call__
res = self.__pydantic_validator__.validate_python(pydantic_core.ArgsKwargs(args, kwargs))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling/document_converter.py", line 237, in convert
return next(all_res)
^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling/document_converter.py", line 260, in convert_all
for conv_res in conv_res_iter:
File "home/path/venv./lib/python3.12/site-packages/docling/document_converter.py", line 332, in _convert
for item in map(
File "home/path/venv./lib/python3.12/site-packages/docling/document_converter.py", line 379, in _process_document
conv_res = self._execute_pipeline(in_doc, raises_on_error=raises_on_error)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling/document_converter.py", line 402, in _execute_pipeline
conv_res = pipeline.execute(in_doc, raises_on_error=raises_on_error)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling/pipeline/base_pipeline.py", line 80, in execute
raise e
File "home/path/venv./lib/python3.12/site-packages/docling/pipeline/base_pipeline.py", line 73, in execute
conv_res = self._assemble_document(conv_res)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling/pipeline/standard_pdf_pipeline.py", line 153, in _assemble_document
conv_res.document = self.reading_order_model(conv_res)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling/models/readingorder_model.py", line 410, in __call__
sorted_elements = self.ro_model.predict_reading_order(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling_ibm_models/reading_order/reading_order_rb.py", line 108, in predict_reading_order
page_to_elems[page_no] = self._predict_page(elems)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "home/path/venv./lib/python3.12/site-packages/docling_ibm_models/reading_order/reading_order_rb.py", line 239, in _predict_page
self._init_ud_maps(page_elements)
File "home/path/venv./lib/python3.12/site-packages/docling_ibm_models/reading_order/reading_order_rb.py", line 366, in _init_ud_maps
self.dn_map[i].append(j)
~~~~~~~~~~~^^^
KeyError: 22
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