[ownedbycats]

When converting the file I attached in post above:

Convert book 1 of 1 (The Lesson)
Conversion options changed from defaults:
  cover: 'D:\\Temporary\\Calibre\\temp\\calibre-_z44_d1p\\8ojlq_cz.jpeg'
  output_profile: 'tablet'
  read_metadata_from_opf: 'D:\\Temporary\\Calibre\\temp\\calibre-_z44_d1p\\tfu3b1sa.opf'
  preserve_cover_aspect_ratio: True
  verbose: 2
Resolved conversion options
calibre version: 8.11.1
{'add_alt_text_to_img': False,
 'allow_local_files_outside_root': False,
 'asciiize': False,
 'author_sort': None,
 'authors': None,
 'base_font_size': 0.0,
 'book_producer': None,
 'breadth_first': False,
 'change_justification': 'original',
 'chapter': "//*[((name()='h1' or name()='h2') and re:test(., "
            "'\\s*((chapter|book|section|part)\\s+)|((prolog|prologue|epilogue)(\\s+|$))', "
            "'i')) or @class = 'chapter']",
 'chapter_mark': 'pagebreak',
 'comments': None,
 'cover': 'D:\\Temporary\\Calibre\\temp\\calibre-_z44_d1p\\8ojlq_cz.jpeg',
 'debug_pipeline': None,
 'dehyphenate': True,
 'delete_blank_paragraphs': True,
 'disable_font_rescaling': False,
 'dont_package': False,
 'dont_split_on_page_breaks': False,
 'duplicate_links_in_toc': False,
 'embed_all_fonts': False,
 'embed_font_family': None,
 'enable_heuristics': False,
 'epub_flatten': False,
 'epub_inline_toc': False,
 'epub_max_image_size': 'none',
 'epub_toc_at_end': False,
 'epub_version': '2',
 'expand_css': False,
 'extra_css': None,
 'extract_to': None,
 'filter_css': '',
 'fix_indents': True,
 'flow_size': 260,
 'font_size_mapping': None,
 'format_scene_breaks': True,
 'html_unwrap_factor': 0.4,
 'input_encoding': None,
 'input_profile': <calibre.customize.profiles.InputProfile object at 0x0000028117C9B250>,
 'insert_blank_line': False,
 'insert_blank_line_size': 0.5,
 'insert_metadata': False,
 'isbn': None,
 'italicize_common_cases': True,
 'keep_ligatures': False,
 'language': None,
 'level1_toc': None,
 'level2_toc': None,
 'level3_toc': None,
 'line_height': 0.0,
 'linearize_tables': False,
 'margin_bottom': 5.0,
 'margin_left': 5.0,
 'margin_right': 5.0,
 'margin_top': 5.0,
 'markup_chapter_headings': True,
 'max_levels': 5,
 'max_toc_links': 50,
 'minimum_line_height': 120.0,
 'no_chapters_in_toc': False,
 'no_default_epub_cover': False,
 'no_inline_navbars': False,
 'no_svg_cover': False,
 'output_profile': <calibre.customize.profiles.TabletOutput object at 0x0000028117CB6A10>,
 'page_breaks_before': "//*[name()='h1' or name()='h2']",
 'prefer_metadata_cover': False,
 'preserve_cover_aspect_ratio': True,
 'pretty_print': True,
 'pubdate': None,
 'publisher': None,
 'rating': None,
 'read_metadata_from_opf': 'D:\\Temporary\\Calibre\\temp\\calibre-_z44_d1p\\tfu3b1sa.opf',
 'remove_fake_margins': True,
 'remove_first_image': False,
 'remove_paragraph_spacing': False,
 'remove_paragraph_spacing_indent_size': 1.5,
 'renumber_headings': True,
 'replace_scene_breaks': '',
 'search_replace': '[]',
 'series': None,
 'series_index': None,
 'smarten_punctuation': False,
 'sr1_replace': None,
 'sr1_search': None,
 'sr2_replace': None,
 'sr2_search': None,
 'sr3_replace': None,
 'sr3_search': None,
 'start_reading_at': None,
 'subset_embedded_fonts': False,
 'tags': None,
 'timestamp': None,
 'title': None,
 'title_sort': None,
 'toc_filter': None,
 'toc_threshold': 6,
 'toc_title': None,
 'transform_css_rules': '[]',
 'transform_html_rules': '[]',
 'unsmarten_punctuation': False,
 'unwrap_lines': True,
 'use_auto_toc': False,
 'verbose': 2}
InputFormatPlugin: HTML Input running
on D:\Temporary\Calibre\temp\calibre-_z44_d1p\zq5v6e_0.html
Language not specified
Creator not specified
Building file list...
	Found files...
		 HTMLFile:0:a:'D:\\Temporary\\Calibre\\temp\\calibre-_z44_d1p\\zq5v6e_0.html'
Normalizing filename cases
Rewriting HTML links
Parsing zq5v6e_0.html ...
Forcing zq5v6e_0.html into XHTML namespace
File zq5v6e_0.html missing <head/> element
File zq5v6e_0.html missing <body/> element
Merging user specified metadata...
Detecting structure...
Auto generated TOC with 0 entries.
Flattening CSS and remapping font sizes...
Source base font size is 12.00000pt
Removing fake margins...
Cleaning up manifest...
Trimming unused files from manifest...
Creating EPUB Output...
Splitting markup on page breaks and flow limits, if any...
	Looking for large trees in zq5v6e_0.html...
	No large trees found
This EPUB file has no Table of Contents. Creating a default TOC
EPUB output written to D:\Temporary\Calibre\temp\calibre-_z44_d1p\jh655vr8.epub

Interesitng the parts about it missing head and body element.

Converting to text made an error saying 0-byte file and the converter probably crashed.