For reference - so community can try and reproduce - please point to the AEM docs you are following for this use case.

For AEM 6.3 - you are using static templates. Sounds like something is wrong with the static template. See if you can get the AEM 6.3 Toy Store (which uses static templates) working: Scott's Digital Community: Creating your First Adobe Experience Manager 6.3 website

This does not make sense - as they are both the same software versions and same API call. Can you show your entire code so the community can see if they can spot something,

See this article which works fine on 6.4. To convert to AEM 6.3 - use the AEM 6.3 UBER JAR file as opposed to the 6.4 one. Creating an Event Listener for Adobe Experience Manager 6.4

Even though it's possible to use APIS to develop pages - its best practice to build an AEM muliti-page site using editable templates --  as discussed in this Adobe document - Getting Started with AEM Sites - WKND Tutorial

We passed this question to the team.

Typically Pages are ordered under content based on how the site is setup in site admin. You can work with pages via the PageManager API - PageManager ("The Adobe AEM Quickstart and Web Application.")

This is not new - been around since 2014. We have plenty of docs on this - see this: Adobe Experience Manager Help | Querying Adobe Experience Manager 6.4 JCR data using the QueryBuilder API

The granite/coral multifield does store data in NODE format:See this article to learn how to work with granite/ui/components/coral/foundation/form/multifield.https://helpx.adobe.com/experience-manager/using/aem64_coral_resourcetypes.htmlHope this helps....

This looks like an upgrade bug - this will not happen on a fresh instance of AEM. Please open a support ticket,