Flattening Issue

[Madeline]

Please help me figure out how to be sure each page of my AD export to PDF (flatten) really gets flattened.  The publisher showed me that some pages are not getting flattened and causing a shift to RGB from CMYK.

 

I am a novice; please guide me through the correct export process to resolve this problem.  All I did in exporting was choose the preset 'flatten'.  I did not click  on the 'more' box (except to look and be overwhelmed) because I have no understanding of those options.  Perhaps it is one or more of these options I need to choose.  And I need to be sure everything stays in CMYK, which is how I created each page of my artwork in AD

 

I attached the screenshot they sent me.

Thank you so much!  

 

Here is the message from the publisher.

 

"As far as the color, some pages are converting to RGB, and others are staying in CMYK.

For better understanding, I have attached a screenshot in wireframe mode of PDF pages 40-41 showing that pg 40 is flattened (one, large image - looks like an "X" across the whole page), while page 41 is showing multiple transparency boxes. 

You will need to make sure all pages are in the same color profile, flatten, and re-upload a new interior if you are not happy with the colors."