Hi @outpost33,
Glad it’s okay now, but allow to explain further as I intentionally skipped the base font size calculation. I only use the 20px size as a sample (after the root size + rem calculation). This is to prevent further calculation and a longer explanation which will be more confusing. As @Christian says, it still has a size of 1.375rem on that page.
The root font size is 16px regardless of the page, either the global builder or on that page. But given that page has 1.375rem, then 16px will become 22px. Please check this another tool https://www.ninjaunits.com/converters/pixels/rem-pixels/

The root font size is just a base font where all local scaling font will be calculated from. I just made a sample of 20px to make the explanation shorter. Hence, in a page with 16px root size with content scaling size of 1.375rem, the base became 22px, so the 0.95em equivalent to that page is 20px.

I also use the exact 20px as a sample instead of 22px so the change is noticeable and prevent confusion. Because when I add 1.375rem, it became 20px too.
While in the global block builder, the root size is still 16px without page local size of 1.375rem. Hence, the 0.95em of 16px is 15px. And it’s by 5px difference to the size you’re comparing.
But yes, you could also use REM as @christian_y recommended, or Pixel too if you wish to apply static sizes regardless of view. I just explained it to say it’s not a bug, and how EM works compared to other units 
Thanks!