I ran into a similar problem, possibly due to migrating from AWS S3 → local → DO Spaces. I ended up up writing some ruby code to manually replace old broken upload urls with the working updated url format and it seems to have fixed my problem.
In my situation, all files were successfully moved to DO Spaces in my first migration, but the migrate_to_s3 logged them as failures. This didn’t break attachments at first, but running a rebake caused them to break. More details in the linked topic.