[Plugin: User Photo] Won’t serve photo

I am trying to insert a photo on a page, but WP won’t even serve it up.
Imagine a user Joe Bloggs; I upload a jpeg and a thumbnail is created. I can get the image https://blog.tld/wp-content/uploads/userphoto/jbloggs.thumbnail.jpg but not https://blog.tld/wp-content/uploads/userphoto/jbloggs.jpg. I get a 500 error.

Both images exist. If I move the full size image to another folder, it is accessible. The thumbnail shows up in the user profile page, but not the full size. This is the case for all users in all roles. Anyone know why these specific images can’t be requested?