Just a complete guess in the dark here, but my initial thoughts are that you’re putting everything into either the header or footer areas which are global to each page, and not the dynamic area which changes.
So, when you construct page 2, it’s overwriting page 1 with the global areas - if that makes sense.
It’s a bit vague until you look closely, but on both the main construction page, and the list on the left, there are 2 blue lines (blue start of names in the list view). The dynamic area is all of the blocs you place between these blue lines, header global being above, footer global being below.
It might be a thought for @Norm to introduce a subtle blue background colour to differentiate the areas until a bloc is added.