PDF Extract Fails On Document With Form Fields

Hi,

 I've tested PDF Extract both in .Net and in Python on this simple form (attached). It always fails on 

FileRef result = extractPdfOperation.Execute(executionContext);
or in Py
result: FileRef = extract_pdf_operation.execute(execution_context)

The Api works fine on documents without form fields, but when those are present, it fails. Here's the error message as shown from a Python script:

INFO:adobe.pdfservices.operation.pdfops.extract_pdf_operation:All validations successfully done. Beginning ExtractPDF operation execution
ERROR:root:Exception encountered while executing operation
Traceback (most recent call last):
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\pdfops\extract_pdf_operation.py", line 134, in execute
    ExtractPDFAPI.download_and_save(location=location, context=execution_context, file_location=file_location)
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\internal\service\extract_pdf_api.py", line 48, in download_and_save
    response = CPFApi.cpf_status_api(location, context)
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\internal\api\cpf_api.py", line 86, in cpf_status_api
    response = polling2.poll(
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\polling2.py", line 191, in poll
    val = target(*args, **kwargs)
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\internal\api\cpf_api.py", line 87, in <lambda>
    lambda: http_client.process_request(http_request=http_request,
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\internal\http\http_client.py", line 42, in process_request
    if _handle_response_and_retry(response, success_status_codes,
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\internal\http\http_client.py", line 105, in _handle_response_and_retry
    raise OperationException(message="Error response received for request",
adobe.pdfservices.operation.internal.exceptions.OperationException

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\Users\Tomek\Documents\Py Code\PDF_Text_Extr_Py\project\extract_txt_tbl.py", line 56, in extract_txt_table_info_from_pdf
    result: FileRef = extract_pdf_operation.execute(execution_context)
  File "C:\Users\Tomek\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\adobe\pdfservices\operation\pdfops\extract_pdf_operation.py", line 138, in execute
    raise ServiceApiException(message=oex.error_message, error_code=oex.error_code,
adobe.pdfservices.operation.exception.exceptions.ServiceApiException: description =ERROR - Unexpected error; requestTrackingId=jtJH99UOppndDZwaTCv2ZXqYDwC8u8hI; statusCode=500; errorCode=UNKNOWN       

 Why am I seeing this error? How to get around it?