iOS fails to properly open unsanitized PDF.

I have a scanned PDF file OCRed from 3rd party software (ScanSnap's ABBYY) that opens without a problem on Windows 10, both on Acrobat Reader or Drawboard PDF but fails to open properly on iOS default PDF viewer and other PDF apps.

Actually, it does open up the file and most of the pages are fine but some of the pages are just blank without any information, thus not opening up properly. 

I thought it was weird so at first I deleted all hidden information (Metadata, Hidden Text, ) from PDF with Tools > Redact > Remove Hidden Information. But this didn't solve the problem and iOS still failed to read all the pages of the PDF.

However, when I tried Sanitize Document option instead of Remove Hidden Information, it magically solved the problem so that the PDF could now have all pages intact on iOS.

This confuses me. I thought 'Remove Hidden Information' and 'Sanitize Document' were basically the same, after reading a thread: Acrobat DC - How Does "Sanitize Document" Differ from "Remove Hidden Information"?

However, it does not seem to be the same since two actions gave different results.

So my questions are:

Q1: What is the difference between 'Remove Hidden Information' and 'Sanitize Document', really? What's happening under the hood?

Q2: Why is my file not read on iOS properly unless I sanitize it? What are the suspected compatibility issues preventing the PDF file from opening on iOS? What may be the solution?

I love Adobe Acrobat DC but sometimes PDFs are just a pain in the ass.