I did a quick local experiment and observed that credentials created from the UI indeed become invalid if you delete the ClearML volumes.

• starting docker-compose locally
• creating a set of credentials from the UI
• hardcodign those credentials into the docker-compose file
• restarting
• the agent-services container started up and successfully became a registered worker
• I killed the docker-compose and deleted the volume folders
• restarted the docker-compose (with the same hard-coded credentials)
  The resulting logs from the agent-services container were this:

Using environment access key CLEARML_API_ACCESS_KEY=NL0V1RKGB0TN57L3OZRK
Using environment secret key CLEARML_API_SECRET_KEY=********

clearml_agent: ERROR: Failed getting token (error 401 from 

): Unauthorized (invalid credentials) (failed to locate provided credentials)