We've been trying to get scripted pipelines to run steps inside docker images for a while now. Steps like bat, powershell, pswh, etc. would cause the build to hang.

After a lot of investigation the issue is soo easy to reproduce!
In Jenkins under "Configure System" > "Global properties" > "Environment variables" we had a variable that contained quotes and a space. Example: "C:\Program Files\Red Gate\SmartAssembly 7\SmartAssembly.com"

Here's a snippet from our Jenkinsfile:

stage('build') {
    echo "On agent"
    docker.build("${appName}:${env.BUILD_ID}").inside {
        echo "In docker"
        bat 'echo running inside docker' // This will hang the build
    }
}

(Note: Using docker.image had the same result.)

Removing the environment variable resolves the issue.