When you export a Normalized PDF or Fast Impose .imp to Adobe PDF, random pages have text converted to outlines even though Contourize fonts is disabled in the ticket.
When you view the exported PDF in an editing software (e.g.: Adobe® Acrobat® Professional, Neo, PackEdge), you see that the text is comprised of outlines wherever the input Normalized PDF has editable text characters.
This may occur where the live text interacts (overlaps or is immediately adjacent to) other artwork and PDF Version 1.3 is chosen in the Export ticket.
Use Default Automation Engine ticket Export to PDF with PDF 1.6 to keep live text from being converted to outlines (flattened).
This solution assumes that Contourize fonts in the Advanced tab is disabled (set to 'Embed BG, Type 1 and CID fonts).