TOC / LOP links are inaccurate; updating individually or from book doesn't work

I have the weirdest problem with links for headings in a TOC or LOP not going to the correct location. For example, I have created chapter TOCs and LOPs and some of the markers on the headings in both the TOC and LOP don't go to the right location, even though I know the file is updating because I've tested adding text to the heading.

I was alerted to it because the links were wrong in the PDF, but the links/markers are in fact wrong in the FrameMaker file, even the text and page numbering is correct. For example, if I add a word to the heading and update the book, or the TOC, or the LOP, that change is reflected. But when I Ctrl + ALT + click on the troublesome heading in the FrameMaker TOC or LOP, it goes to an incorrect location in the chapter. For example, I'll do Ctrl + ALT + click on the heading in the LOP or TOC and it'll take me to a body paragraph and about 20 pages before the right location. I don't understand how a marker could even be created this way (I'm assuming it's a marker). I even created a new standalone TOC for the chapter, added it to the book, updated the book, and still in accurate. It's like a chunk of headings within the list/TOC just keep pointing to text elsewhere in the chapter for no reason; there are no markers on that page that I can see. The only pattern I can determine is that the same destination pages are used, but sometimes different paragraphs or table headings or something I can't even see (nothing is highlight).

Do I have to rebuild the whole darn chapter? This is a massive manual as it is and I don't have a lot of time either. Traditionally, I had faith that the TOCs and LOPs would be accurate as long as I updated the file/inserted the TOC/LOP/updated the book because that's how it normally works (and currently works except for this random issue), but now I'm looking at having to manually check thousands of headings, and then I have no idea what's even causing this issue in the first place!