If you're having the same issue experienced in this post it's highly likely that in between the database restore occurring and the jobs starting a log backup has been taken, either by an admin or by another running backup job, and not transferred to the secondary server.

Once log shipping has been implemented for a database all log backups must be done via the log shipping plan and not via any external jobs\processes.

Please create a new post in future, it helps you and others 😉