Problems Converting HTML to EPUB

[ezechias]

Hi, for years I have been converting HTML files to produce both AZW3 and EPUB files for two different readers (Kindle Paperwhite & FBReader on Pixel phone) Recently, however, converting the HTML to EPUB produces an empty document. The same file produces AZW3 just fine, so when I convert the AZW3 file to EPUB, it also comes out fine, but the end section is missing. I have attached 4 files. The original HTML file, the empty EPUB, the good AZW3 and the EPUB converted FROM the AZW3 which has the missing end section. I am using portable Calibre 9.16.0 on and an up-to-date Windows 11 machine. The only settings I am changing are device format to Paperwhite 3, linearize tables, no table of contents, and this extra CSS: body {text-align: left;}
p {text-align: left;}
Thanks for your help.

[DNSB]

As near as I can tell, your .zip file is close to a .epub file. If I change the name to RB1016.epub, calibre imports it as "Divinum Officium Matutinum - RB1016.epub". OTOH, this is supposedly an ePub2 file so a NCX navigation file needed to be added, the javascript needs to be removed and the CSS in the HTML file is not suited to an ereader as it makes much use of obsolete items. There are also a mass of embedded links to external content which gives me a security error (Sorry, you have been blocked You are unable to access divinumofficium.com).

Anyhow, had nothing better to do for 15 minutes since the granddaughter is still napping so did some cleanup on the renamed .zip file. It's attached to this message.

In future, you might want to use a browser plugin to download the webpage and handle quite a bit of the cleanup.