Did you do the migration to the shared library or the individual application?
Also, can you open the application in app library and do a compare to the "shared library" to check if there are any differences?
To answer your questions:
A) I did migrate the shared dimensions in the shared library first and then the planning settings. Importing the planning settings should have overwritten the aggregation property in the application, which it did but just for the members without a description.
B) There are differences between the dimension in the app library and the shared library, as expected. That is exactly due to the aggregation properties that have been set up differently on the app library.
Can you check the xml (for the planning settings) to see if it has any issues for the members with descriptions? Are the descriptions simple text or do they have any special characters?