This secondary database is not functional because the required copy or restore job cannot be found. You must remove this ...

This secondary database is not functional because the required copy or restore job cannot be found. You must remove this secondary database by clicking Remove. To resume log shipping to this secondary database, add it as a secondary again using the same settings.

If you resume log shipping and you specify the same restore path that you used before, any backup files that are uncopied or unrestored to this database will be copied and restored when it is added as a secondary again.  Reinitializing the secondary database is unnecessary.