Why is converting to PDF deleting some of my Illustrator pages?

[Sarah356061648o5x]

I have an illustrator file with just one layer. It contains 4 separate blocks / pages which will come together at the printing press to create an embossed flyer (printed in multiple stages, hence the 4 separate pages).

The printer only accepts PDF files.

When saving the Illustrator files as PDF, the last two pages disappear. 

The file is super simple, the first two pages are the base CYMK colour with no text or images. These export to PDF perfectly.

The last two pages contain the rasterised images. These do not export at all, they just cease to exist. 

I've attached a screentshot of the Illustrator page. 

Any ideas?

[Monika Gause]

And those are artboard?

Please show your export settings?

Which PDF viewer are you using to check the file? If not Acrobat, please use that.