Hi,
Internally EO.Pdf uses a pool of WebView objects to perform the conversion. So unless you explicitly maintains sessions with HtmlToPdfSession object, session data can be mixed together between conversions. In this case you should use HtmlToPdfSession object instead.
If you still have problem, you can send the test project to us and we will investigate further. See here for more details:
https://www.essentialobjects.com/forum/test_project.aspxThanks!