@Matt Lawton There is known issue in F0 limit of projects. Basically recently we have done a pretty big backend change and just deployed that. So this deployment caused the regression. The setting for F0 limit of projects are set wrong.
We Will deploy the fix as soon as possible. we would recommend to raise a Azure support desk ticket from Help+Support blade from Azure portal for your custom vision service resource. . This will help you to share the details securely and work with an engineer.