Thanks Jesse Glick and An Tran for digging into this more! I personally am not concerned whether or not this is a bug or improvement, as long as it is fixed . It does sound a lot like a bug to me, but I do understand the argument for it being an improvement. Whatever the best path to resolution is will be fine with me.

Based on the tickets An Tran linked above, it looks like others desire this functionality as well.

I am also stuck in the same situation, where I need to use scripted parallel block within declarative and the blueocean view is doesn't display the stages for scripted block correctly.

Here I share three code examples (bottom of this comment)

1. declarative parallel within declarative pipeline
2. scripted parallel within scripted pipeline
3. scripted parallel within declarative pipeline

The first two get visualized as expected.

The third one gets a messed up visualization starting at the parallel part, i.e. also affects the next non-parallel stage.

The code

• declarative parallel within declarative pipeline

  pipeline {
      agent("none")
      stages {
          stage("prepare") {steps {echo "prepare"}}
          stage("build") {steps {echo "build"}}
          stage("test") {
              parallel {
                  stage("linux") {
                      stages {
                          stage("install") {steps {echo "installing in linux"}}
                          stage("test") {steps {echo "testing in linux"}}
                      }
                  }
                  stage("windows") {
                      stages {
                          stage("install") {steps {echo "installing in windows"}}
                          stage("test") {steps {echo "testing in windows"}}
                      }
                  }
                  stage("mac") {
                      stages {
                          stage("install") {steps {echo "installing in mac"}}
                          stage("test") {steps {echo "testing in mac"}}
                      }
                  }
              }
          }
          stage("cleanup") {steps {echo "cleanup"}}
      }
  }
  

• scripted parallel within scripted pipeline

  stage("prepare") {echo "prepare"}
  stage("build") {echo "build"}
  stage("test") {
      parallel ([
          "linux": {
              stage("install") {echo "installing in linux"}
              stage("test") {echo "testing in linux"}
          },
          "windows": {
              stage("install") {echo "installing in windows"}
              stage("test") {echo "testing in windows"}
          },
          "mac": {
              stage("install") {echo "installing in mac"}
              stage("test") {echo "testing in mac"}
          }
      ])
  }
  stage("cleanup") {echo "cleanup"}
  

• scripted parallel within declarative pipeline

  pipeline {
      agent("none")
      stages {
          stage("prepare") {steps {echo "prepare"}}
          stage("build") {steps {echo "build"}}
          stage("test") {
              steps {
                  script {
                      parallel ([
                          "linux": {
                              stage("install") {echo "installing in linux"}
                              stage("test") {echo "testing in linux"}
                          },
                          "windows": {
                              stage("install") {echo "installing in windows"}
                              stage("test") {echo "testing in windows"}
                          },
                          "mac": {
                              stage("install") {echo "installing in mac"}
                              stage("test") {echo "testing in mac"}
                          }
                      ])
                  }
              }
          }
          stage("cleanup") {steps {echo "cleanup"}}
      }
  }

   

I have the same problem mentioned by Alberto Arango. With a scripted pipeline inside a declarative one, BlueOcean gets confused.
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I am using a scripted pipeline inside a declarative one because I need to spawn multiple parallel jobs according to some dynamic variables. Using Matrix/Axes I cannot do it.