I *think* the answer to this is because of the differences between viewing courses on your phone vs. on a computer. What I mean is...your instructor may not yet have "published" your course and/or set the dates for the course to allow you to see the content via a web browser, but in the app, you are still able to see your courses that you'll be taking this Spring. I seem to recall this being the case when I did my own testing within the Canvas app several months ago. My guess is that when you are using a computer and sign in to Canvas, you can go to your "Courses" (or "Courses & Groups") menu, choose "View All or Customize", and you'll see your courses listed under "Future Enrollments" which means the courses haven't started just yet...but they will once your semester starts and your instructor "publishes" the courses.
Also, I am going to re-label the subject line of your question so that it is a bit more specific to what you are asking in the body of your message. I'll also tag your message with keywords so that others can find your question easier here in the Canvas Community. Please let me know if the revised subject line doesn't reflect what you are asking in the body of your message. We can make any needed changes at any time. Hope this is okay with you, and hope this helps!
My next thought would be to contact someone at your school who works with Canvas on a day-to-day basis that could tell you if you are properly enrolled in the courses you'll be taking this semester. (Or, maybe there is an Online Learning or similar department at your school where you could seek assistance.) If you are properly enrolled, maybe there is a chance that your instructors have not yet set the date and access properties for the courses yet so that you'd be able to see them.
jscanlon, we haven't heard from you in a while, and are hopeful that you are now able to view your courses both on your computer and mobile. We'll move this question to "Assumed Answered" status. Please feel free to provide an update to let us know how you're progressing.
Belatedly chiming in: earlier this week, one of our students had a similar issue. She said she could see the course in iOS Canvas but on her computer it was showing as unpublished. When I masqueraded as her, I could see the same problem, so I knew it wasn't a student browser issue, etc. I fixed the problem by removing her from the course and then re-adding her. Perhaps that will solve this problem. I didn't report it to Instructure support because it was a one-time event and I wanted to give her a quick resolution. If the problem persists, I will report it in the future.
I am the professor and I am having this problem. I have published my courses, it is mid-semester, and I have not had this problem to date. The only recent change is that I was added as a teacher to another professor's course. Please advise as soon as possible.