Create a pipeline with the following configuration and run the job.

pipeline {
    agent {
        label 'my_label'
    }

    triggers {
        upstream upstreamProjects: 'upstream', threshold: hudson.model.Result.SUCCESS
    }

    options{
        timestamps()
    }

    stages {
        stage('build') {
            steps {
                echo 'building'
            }
        }
    }

Create another job (upstream) in the same folder and run it (should see original pipeline is triggered).

Remove triggers from original pipeline, rerun it (to ensure a new config.xml could be generated)

Rerun upstream job

The second run should trigger the pipeline job. What I've done in the past to workaround this is to put in a bogus upstream job in triggers to force a rewrite of config.xml.