None of the relevant modules or folders have lock dates or restrictions. I did find a work-around, however. If I delete all the files, and then upload them directly to the module, the students can see them.

Then I deleted them again. Then I uploaded them to the file section and then added them to the module from the file area. That is the problem. The only way the students can see them is if I skip the file section and upload the files directly from my computer to the module.

Still, Canvas should let me upload a file from my machine to the file area of Canvas, then populate modules with those files.