Items need to be valid embed fields because you're using PaginatedFIELDMessageEmbed and fields need a description, title and whether it's inline or not, no other fields. You cannot just insert a random object and expect it to me magically mapped. The error tells you the title is missing and yes it clearly is missing.
You should either make a 2 dimensional array of titles and descriptions to ensure every page has an array of proper structure OR use PaginatedMessageEmbed root class and build your own pages with addPageEmbed