I ran across this article which could potentially shed some light on your situation:
The bottom paragraph might be the issue:
Print to PDF exports blank PDF page
When working with certain sheets in Tableau Desktop, using the Print to PDF option may export a blank PDF. This issue occurs when you print very large sheets using the Unspecified paper size option. A sheet that is larger than 32,668 pixels in width or height, and whose paper size has been set to Unspecified will export a blank PDF. To resolve this issue, you must specify a different paper size before using the Print to PDF option. Alternatively, consider decreasing the pixel width or height of the sheet by possibly reducing the information displayed in the view.
thank you Ben, found the issue.