In some cases when you have a parallel branch finish early, this won't show up as completed until the whole stage completes.

Looking at the following recording:
http://www.giphy.com/gifs/3oz8xtmarVuXWqfug0

The right branch finishes after 1s, but doesn't show up as completed until I click on it.

The pipeline to reproduce this:

node {
    stage("first") {
        sh 'ping -c 3 www.apple.com'    
    }
    
    stage("second") {
        parallel (
            "left" : {
                sh 'ping -c 10 www.apple.com'            
            }, 
            "right" : {
                sh 'ping -c 1 www.apple.com'    
            }
            )
        
    }
    
    stage("third") {
        sh 'ping -c 3 www.apple.com'    
    }
    
}

this sometimes does work. This also depends on the https://github.com/jenkinsci/blueocean-plugin/pull/557 being merged, which uses the new bismuth api.
There is likely some front end code that can be simplified.