Issue with gitlab-runner for multiple projects with concurrency

We have a gitlab-runner registered to our group where we are running multiple cicd jobs from multiple projects. After updating concurrency in config.toml file from 1 to 10 we are facing issues with the jobs running because it created multiple build folders like builds/0 , builds/1 , builds/2 etc due to this different jobs in pipeline are running in different folders. not sure what we are missing here, could someone help ?