A matrix job where some stages are excluded is showing some of the stages as "skipped" in the Blue Ocean UI, or as having no steps in the traditional UI.
The logs are showing that the steps have been run as expected.
Even if a step fails in a stage, it does not show up in the UI.
This makes the Jenkins Web UI useless for tracking the progress of a Matrix job.
Attached is a Jenkinsfile that reproduces the problem with a single stage in the Matrix step.
If more stages are added to the step, some of those additional stages are not shown on the web UI.
This looks similar to: