why does the User and Group Preferences Export does not always export all user preferences?
The import/export functionality was designed so as not to import user filters, if filters have already been set on the user that is importing.
This is FAD but it is possible to manually work around this, by using CLI to delete the existing filters, on the user importing, before proceeding.
With vnmsh connected to CLI, use the command
./update mh=<model_handle of user> attr=0x129ef, val=""
This clears the setting for user preferences and filters can be then imported however, personal filters are lost.