If you find yourself relying on restic using rclone to talk to non-default regions you may want to check out the just released restic version 0.9.6. To me it appears to be fixed when working with Oracle Cloud Infrastructure (OCI) object storage. Below shows a test accessing Phoenix endpoint with the new -o option.
# restic -r s3:<tenancy_name>.compat.objectstorage.us-phoenix-1.oraclecloud.com/restic-backups snapshots -o s3.region="us-phoenix-1"repository <....> opened successfully, password is correctID Time Host Tags Paths----------------------------------------------------------------------------------------f23784fd 2019-10-27 05:10:02 host01.domain.com mytag /etc