Progress of a sort, it seems to be a backend issue, not a front-end issue like I first thought. Switching focus there

Righto, good progress, I've built a minimal pipeline that generates the issue reliably, and figured out the trigger: https://gist.github.com/sophistifunk/39cec79eb7d353b67bd70b75a61f95bc

It seems that any time you have all of these conditions:

1. A parallel stage
2. The last parallel branch (in file order) is nested in a sequential wrapper, ie:

   stage('foo') { stages { /*...*/ } }

1. The sequential wrapper only has one child stage

Then the generated graph data is broken for nodes coming after the offending top-level stage.

The problem is (almost certainly) in Blue Ocean server, or (far less likely) the Pipeline plugin. I'll find out which one and get a fix in, should be a small change once I identify the right spot.

PR (waiting on some dogfood issues for building) https://github.com/jenkinsci/blueocean-plugin/pull/1836

Fixed in master @ e49553f1c8792e4e6f74285d3f8377a8f4ec3d99

thank you sophistifunk!

Can you please help me with JENKINS-53735 since noone is replying ?