Go to this page on an ipad: http://www.quirksmode.org/css/css2/overflowscrolling.html
I am on iOS 10, Safari 10.0.
Usually the first time it loads the scroll bars are not visible. Then resfreshing the page will bring them back. Clearing the cache may be necessary.
I got the link from a discussion question created for the same issue: https://discussions.apple.com/thread/7022910?start=0&tstart=0
I assume you mean the scrollbars in the second scrollable area, and them not being visible when scrolling that area?
Yes you are correct.