Viewer error on HTMLZ files

[aldsjf(*&12]

Hi,

I recently upgraded from Ubuntu 20.04 to 22.04 and reinstalled Calibre. Since then the e-book viewer gives this error when I try to open HTMLZ files:

calibre, version 6.26.0
ERROR: Loading book failed: Failed to open the book at [...PATH TO FILE...]. Click "Show details" for more info.

Failed to convert book: [...PATH TO FILE...] with error:
InputFormatPlugin: HTLZ Input running
on [...PATH TO FILE...]
Multiple HTML files found in the archive. Only index.html will be used.
Language not specified
Creator not specified
Building file list...
Normalizing filename cases
Rewriting HTML links
Forcing index1.html into XHTML namespace
Failed to run pipe worker with command: from calibre.srv.render_book import viewer_main; viewer_main()
Traceback (most recent call last):
  File "runpy.py", line 196, in _run_module_as_main
  File "runpy.py", line 86, in _run_code
  File "site.py", line 47, in <module>
  File "site.py", line 43, in main
  File "calibre/utils/ipc/worker.py", line 196, in main
  File "<string>", line 1, in <module>
  File "calibre/srv/render_book.py", line 830, in viewer_main
  File "calibre/srv/render_book.py", line 821, in render_for_viewer
  File "calibre/srv/render_book.py", line 799, in render
  File "calibre/srv/render_book.py", line 612, in process_exploded_book
  File "calibre/srv/render_book.py", line 274, in create_cover_page
  File "calibre/ebooks/oeb/polish/container.py", line 956, in generate_item
IndexError: list index out of range

Before the upgrade, HTMLZ files opened without problems. Any ideas how to fix this/any workarounds? I want to use HTMLZ because it can smooth-scroll (rather than jump) over chapter boundaries. Thanks.

[kovidgoyal]

Open a bug report and attach one of these failing files.

[aldsjf(*&12]

Submitted Bug #2040439 on bugs.launchpad.net