Hi there,
Sorry to hear about this trouble. Is the issue related to a specific document? If yes, could you please share the document with us? You can upload it to the Creative Cloud (https://helpx.adobe.com/in/creative-cloud/help/share.html) and share the download link.
Also, please share a screenshot of settings you are using to save PDF from Illustrator.

We’re here to help, just need more info.
Regards
Srishti