We have encountered a serious bug in the import of Meta Box Groups. This seems to be related to the WYSIWYG field, though it may apply to some other fields as well. The result is a silent failure to import the post meta.
You can duplicate this by downloading the demo files from and taking the following steps.
In an instance of WordPress with the required Meta Box plugins first import the group-bug-demo-post-type.xml using the WP importer. Then import the group-bug-demo-fields.json file with the importer in Meta Box Custom Fields. And finally, import the group-bug-demo-pages.xml using the WP importer.
Now go look at the "Test Book" in the "Group Bug Demo Books" post type. Notice that it has a "Group Bug Demo" section that is empty.
Now open the group-bug-demo-pages.xml and verify that there was, in fact, post meta for that post that was not imported.
In fact, on the original website where this data was created, the "Test Book" displays this metadata just fine. You can see the group-bug-demo-original.jpg file for a screenshot. Or you can repeat the experiment for yourself by creating a new test book with similar descriptions and then exporting those.
My guess is that the problem is due to linefeed characters in the WYSIWYG field. I have manually removed these characters and adjusted the PHP serialization in the group-bug-demo-fixed-pages file, and that one imports without the error.
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