Unsurprisingly, when exporting it will only export what is currently in memory. So, if your chat extends many, many pages, dont expect those other pages to be exported. So you would need to get all the pages in memory first, then you can export.
Also, it seems way to heavy in wanting you to upgrade, which is usually a bad sign for the future.
Overall though the pdf export quality is done respectably by preserving fonts/images/layout (as best it can, at least).
