Ok, in this case I assume you have somewhere still a configuration for the dimensions, which you are not aware of. Do you have the Demo-Site installed?
Please check the configuration with following command:
./flow configuration:show --path Neos.ContentRepository.contentDimensions
This should be empty (if you set the cofiguration empty as above mentioned).
Configuration "Settings: Neos.ContentRepository.contentDimensions":
{ }