Search Results Snippets for PDFs - some include highlighted keyword matches, some don't

[lh435]

Hi,
We are indexing and searching a bunch of PDFs. Currently in the results page, many items show the relevant text with highlighted keyword matches, which is what we'd like, but some of them don't – instead, they show text from the beginning of the document.

From the latter group, if I open the PDF individually and search with command-F, the term does appear in the body of the document, so I know it's in there.

How might I get all the search results to show the relevant snippets?

The config file includes:
query_processor_options=-stem=2 -SF=[f,d,c,title] -SBL=1500 -MBL=1500

I also tried adding "-SM=qb" to those options.

Thank you for any suggestions!

[lh435]

This is also true when I look in the cached version of the PDF's text (via the caret in the search results) – even when the keyword does appear in the cached text, it sometimes does not appear in the item's search summary.