We use restic dump | tar -xf - to restore files.
When the cache is missing, restic adds the cache creation message created new cache in ... at the beginning of the tar archive, breaking the expected format:
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Exiting with failure status due to previous errors
As a workaround, I use the --json option to disable the message, but I think it’d be better not to break the tar format, avoiding extra output if the format is tar.
I didn’t test zip format.
More details in this github issue for NethServer.