Recent quotes:

Amazon Claims to Accurately Measure Pages Read in Kindle Unlimited, Neglects to Mention There's no Standard Page Size | The Digital Reader

The thing is, folks, if one page in Book A is equal to 1.2 pages in Book B and 0.8 pages in Book C then it really doesn't matter how carefully Amazon counts the pages. Any count reported by Amazon is fundamentally bullshit because there is no single standard page size. Let me phrase it another way: Amazon's accounting system in Kindle Unlimited is broken on a fundamental level.