CumulusCI executes commands against the org whose name you specify with
--org. If that org does not yet exist, CumulusCI creates an empty org and executes the command against it.
Before running tests, whether Robot or Apex, with CumulusCI, you'll typically build the org using a flow, such as
install_beta. Those flows push your project's unmanaged code into the org (
qa_org), or install a managed beta (
install_beta). For Robot tests, it's common to do something like
cci flow run qa_org --org dev
cci task run robot --org dev [...]
That builds the org first and then runs Robot tests against it.
If you think you've already built the org, perhaps you run the building flow in a different CircleCI container than you're running the
robot task? If that's the case, your CumulusCI in the Robot context may not have access to the details of the created org, and you'd need to persist it using Circle's workspaces feature.
(Disclosure: I am on the team that builds CumulusCI at Salesforce.org).