I think whoever created these books deserves a slap.
I would say there is nothing else to be done, but... thing is, I was unaware there was any other way to identify chapters. Clearly, my Kindle disagrees with me, and for that reason alone it *might* be worth investigating and possibly utilizing that instead. Then again maybe it isn't really worth trying to fix for a clearly broken book.
Perhaps it is working off the page-breaks??? At least I can see the swipe-to-switch-chapters working that way, but the Go To menu is a puzzle.
Since I don't really know a lot about mobi7/8 internals, I am not going to try answering this mystery.