Thanks for all the comments so far. Let me address some of the points to the best of my ability.
First off, @EarnestAI linked the StackOverflow post I was referring to. Appreciate it, I didn’t know whether cross-linking outside sources was against community guidelines so I refrained from doing that - that is exactly what I meant when I was referring to this being “a known issue” and the by-paragraph “fix”.
@mikekaganski , on your follow-up questions:
I do not know what is causing the issue - if I would, I probably would know how to fix it myself. I have an enormous ODT file - and if I ever do another project of this magnitude, I definitely wouldn’t use LibreOffice for it but rather something like Scribus. The file is 391-397 pages long - rendering is totally random and breaks the formatting every single time the file is opened, something I posted about a while back, and using sections didn’t fix this -, and is 484MiB in size. I am happy to link it, but I cannot just surgically make a copy of the problematic section and share it here because I do not know where it is. (Assuming it’s a “localized” issue.)
@Wanderer , to your points:
Appreciate the link to the flattening guide, I’ll check with my girlfriend, she has an Adobe subscription with access to Acrobat.
On “Search and replace”, if you check what the other user did ( How can I fix the PDF preflight error: "The 'Widths' array in a font has an invalid length" - Stack Overflow ), they basically went through their whole document, highlight every paragraph one by one, and where the formatting hid the font type implying there’s multiple fonts in the paragraph where there should only be one, they manually updated the font. Out of desperation I actually tried this, but that did not help.
On the freezing up: yes, I am editing an ODT. Again, it’s enormous; it has close to 200 illustrations embedded into it with a lot of layouting, sections, and illustrated textboxes. Past page 200 even clicking on an image to check its properties freezes up LO for a good while, and God save your soul if you are trying to fix the layout on the later pages as LO is struggling to render those. (Yes, I considered chopping the document up into multiple odt files by chapter, but using the master document approach created a hot mess. Again, I know I should have used some proper publishing software, but hindsight is 2020, the document is in its final form, and this export bug is the last thing that prevents me from sending it in for printing.)