When I export my Indesign document to PDF (print or interactive, various compatabilies) I get these random small black lines appear on random pages. Doesn't seem to be associated with certain symbols. Any ideas?
Try resetting your preferences: The easiest way to reset everything is to delete the InDesign preferences: as soon as InDesign starts to boot hold down Shift, Alt, Ctrl (and Apple/Cmd if working on a Macintosh). A dialog will appear asking to delete the InDesign Preferences, select 'Yes' on this dialog. Further info and instructions here if needed: https://helpx.adobe.com/in/indesign/kb/indesign-preferences-support-file-locations.html
If a document is not behaving well then try
Open the IDML in InDesign Save the file as a new InDesign file with a new name See if the issue persists.