IndexError during file transfer

[athens46]

Certain books (about one in a thousand for my library) in the process of being transferred to Kobo will throw up the IndexError below. If the book producing an error is part of a larger transfer job, the IndexError causes the entire transfer to fail regardless of progress on other epubs. I can provide a couple epubs that trigger the issue.

Running 7.23.0. The following user-installed utilities are in use and up to date:
KePub Input 3.6.6
KePub Output 3.7.3
KoboTouchExtended 3.7.3
KePub Metadata Reader 3.4.3
Kobo Metadata 1.9.1
KePub Metadata Writer 3.4.3
Kobo Utilities 2.17.2

Debug log. Full error message below:

calibre, version 7.23.0
ERROR: Error: Error communicating with device

Failed to process What Is Tao? by Alan Watts: list index out of range

Traceback (most recent call last):
  File "calibre_plugins.kobotouch_extended.device.driver", line 188, in _modify_epub
    common.modify_epub()
  File "calibre_plugins.kobotouch_extended.common", line 238, in modify_epub
    container.convert()
  File "calibre_plugins.kobotouch_extended.container", line 398, in convert
    self.__run_async_over_content(self.add_kobo_spans)
  File "calibre_plugins.kobotouch_extended.container", line 394, in __run_async_over_content
    self.__run_async(func, names)
  File "calibre_plugins.kobotouch_extended.container", line 381, in __run_async
    raise e
  File "calibre_plugins.kobotouch_extended.container", line 377, in __run_async
    name = future.result(timeout=60)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "concurrent/futures/_base.py", line 449, in result
  File "concurrent/futures/_base.py", line 401, in __get_result
  File "concurrent/futures/thread.py", line 58, in run
  File "calibre_plugins.kobotouch_extended.container", line 522, in add_kobo_spans
    body = root.xpath("./xhtml:body", namespaces={"xhtml": XHTML_NAMESPACE})[0]
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^
IndexError: list index out of range

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "calibre/gui2/device.py", line 112, in run
  File "calibre/gui2/device.py", line 646, in _upload_books
  File "calibre_plugins.kobotouch_extended.device.driver", line 343, in upload_books
    return super(KOBOTOUCHEXTENDED, self).upload_books(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "calibre/devices/kobo/driver.py", line 2283, in upload_books
  File "calibre_plugins.kobotouch_extended.device.driver", line 212, in _modify_epub
    raise e.__class__(msg).with_traceback(tb)
  File "calibre_plugins.kobotouch_extended.device.driver", line 188, in _modify_epub
    common.modify_epub(
  File "calibre_plugins.kobotouch_extended.common", line 238, in modify_epub
    container.convert()
  File "calibre_plugins.kobotouch_extended.container", line 398, in convert
    self.__run_async_over_content(self.add_kobo_spans)
  File "calibre_plugins.kobotouch_extended.container", line 394, in __run_async_over_content
    self.__run_async(func, names)
  File "calibre_plugins.kobotouch_extended.container", line 381, in __run_async
    raise e
  File "calibre_plugins.kobotouch_extended.container", line 377, in __run_async
    name = future.result(timeout=60)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "concurrent/futures/_base.py", line 449, in result
  File "concurrent/futures/_base.py", line 401, in __get_result
  File "concurrent/futures/thread.py", line 58, in run
  File "calibre_plugins.kobotouch_extended.container", line 522, in add_kobo_spans
    body = root.xpath("./xhtml:body", namespaces={"xhtml": XHTML_NAMESPACE})[0]
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^
IndexError: Failed to process What Is Tao? by Alan Watts: list index out of range