I have now 2 rwmb_meta_boxes added to a settingspage with two tabs.
Instead of tabs I will use a top-level menu page and 2 sub settings pages.
I have add two sub settings paged, it works.
When I change the meta boxes from settings page top to the subsettings page AND remove the tab then the MetaBox shows in the sub settings but all the fields are empty.
What do I wrong?