The Bulk Import module for batch registration of items and media in Omeka S has a bug in versions 3.3.28.0 through 3.3.33.2 that prevents media from being registered. If you need to register media, you will need a workaround such as using version 3.3.27.0 or earlier.
After creating an issue about this problem, the bug was promptly fixed:
As of July 1, only the source code on GitLab has been updated, but it should be added to the GitHub Releases soon. Please be aware of this when using this module.
If you want to install from the GitLab source code, please refer to this README. Specifically, navigate to the modules directory and run commands like the following:
I hope this serves as a useful reference when using BulkImport.