The following sample will intermittently throw NotSerializableException: java.util.regex.Matcher.  However, this code does not directly use a Matcher.  Seems like this problem could exist anywhere when calling any function that internally uses a non-serializable field that is not annotated as NonCPS.

pipeline {
    agent {
        label 'master'
    }
    stages {
        stage('stage') {
            steps {
                script {
                    parallel ((1..20).collect{it}.collectEntries {
                        ["$it": {
                            node('master') {
                                stage("$it") {
                                    sh('')
                                    '.'.replaceAll('.', {})
                                }
                            }
                        }]
                    })
                }
            }
        }
    }
}

Notes:

• The sh step must be done.
• The replaceAll must pass a closure.
• The empty sh and replaceAll closure are not empty in my production pipeline, but are minimized here for a concise example.  (That is, the solution is not "remove code that does not have any effects").
• Seems that the upper end of the range needs to be larger than the number of executors.
• The range must be collected to an Array or it will throw "NotSerializableException: groovy.lang.IntRange", which seems like its own bug as the range is never saved as a field.