Symbols background is interlaced or vanished after PDF-Export

[Anna38935578kzu4]

After exporting my AI-file to a PDF most of the used symbols have an interlaced background. Or sometimes the background is gone.

I had to deal with this problem several times already.

Is there any way to fix this?

 

[Monika Gause]

Are you checking the PDF in Acrobat?

Is there any transparency involved? blend mode? Overprinting? Spot color?

What is this "symbol"? Illustrator objects? A placed image? 

[Anna38935578kzu4]

Thnak you for your quick answer.

The symbols are actually from an *.ai symbol library we once created.

There is no transparency used for the symbols only in other areas of the file. There is also no blend mode used for the symbols or spot colors.

Some symbols are displayed correctly.

The funny think is that it worked beforhand already. I used to create some pdf-files beforehand where it worked normaly and the smybols were displayed correctly. I didn't change anything on the file except relinking the raster background image.

So I m wondering now where it comes from.

[Monika Gause]

Without having the actual PDFs this cannot be solved.

You can try and reset the Illustrator preferences. Maybe something got corrupted. Quit Illustrator and then rename the Preferences folder, since that can be undone