We were having this issue also, and updating to 3.9.8 fixes it.
We were also experiencing issues when a user uses the “Download” button and then clicks the download from their browser to open in a PDF viewer, they were getting “There was an error opening this document. The file is damaged and could not be opened” errors. However, clicking the download icons from the local browser preview, saving the PDF to their Desktop and then opening would work just fine. A similar thing was happening with Excel spreadsheets and newer versions of Office.
The latest update to 3.9.8 seems to have resolved these issues. I’m still testing.