I kinda have the feeling that the process for producing the tablet is quite different from the one used for producing the phone. They ship directly from their Honk Kong Based subsidiary, they seem to get a lot more low level, debugging hardware and supply problems, going quote publicly over more iterations, etc.

Maybe before they basically ordered the whole thing from an OEM and were not satisfied with it so they decided to handle bigger part of the manufacturing themselves ? Or the other way around ?

One has to take account that the Jolla Tablet is a crowdfunding campaign where you re expected to provide much bigger insights into product development and production than with a regular commercial product (Jolla Phone). That can definitely also influence the image one gets of the project.