You may have been invited to Lt by two different departments or institutions with different “Instances”.
You can only see the courses from one Instance at a time, but it is easy to switch between the two. Go to your homepage and look at the logo in the top left hand corner. If you've been invited to multiple instances you'll see a dropdown arrow next to the logo:
Select this to switch instances and view other courses, lessons and modules you have access to. If no dropdown arrow appears next to your instance logo in the top-left of your homepage, you have only been invited to one Instance. Check with the course administrator that your course enrollment details are up-to-date. If your course has finished it is possible that the course provider has now removed your access from this course.