Normally all the Importing of shifts would be done before publsihing.
Import can only be done on weeks that are unpublished. Or if part of the week is published, you can only import shifts for positions that are still unpublished in that week.
If your full schedule or those positions are published on the week you want to Import, you will need to unpublish the positions you want to Import (or fully unpublish) that week before Importing.
import to a published schedule