Hi @cmh and welcome to the community!
If your project has many media files, exporting all media attachments as a ZIP file may fail or take too long. As Kal stated in the post below, I think this is something the core team is working on.
In the meantime you can check the Media attachment ZIP export fails subcategory under the Managing respondent-submitted media - Troubleshooting, which I share in the link below.
Hopefully this works for you.
