Came back the next day and tried again, and the migrate task worked fine. I guess the logo images were never the problem, and it was just those two extraneous ones. Presumably those got cleaned up by some sort of periodic task, because when I look now they’re gone.
In hindsight, the upload task checks for bad upload url’s with:
Upload.by_users.where("url NOT LIKE '//%' AND url NOT LIKE '/%#{seeded_image_url}%'").exists?
Presumably it’s the by_users that causes it to ignore the logo images, since those don’t have a valid user_id.