Your DEV@cloud instance is blocked with a message like:
Your total DEV@Cloud disk usage is over your subscription’s quota. Your subscription ‘XXXXX’ allows YY GB, but you are using ZZZZZ MB across all services (Forge and Jenkins). To fix this, you can either upgrade your subscription or delete some data in your Forge repositories, Jenkins workspaces or build artifacts.
You have to configure your instance to regularly cleanup old builds / archives. See: Deleting Old Builds - Best Strategy for Cleanup and disk space management
You can find useful the simple disk usage plugin ( https://ACCOUNT.ci.cloudbees.com/disk-usage-simple/ ) which allows you to list the space used by your jobs and to run the cleanup command on them.
Your quota also includes the space used by your data stored in your forge repositories. You can see the space are using from https://console.cloudbees.com/a/ACCOUNT/repos/ (Don’t forget to activate the cleanup of old artifacts on Maven SNAPSHOTs repositories)