A pipeline stage with a parallel execution will have the status "In Progress" when it first executes the parallel command.
The status will stay at "In Progress" until the first of the parallel jobs completes.
Once that job completes, the status of the pipeline stage will change to the status of the first successful job.
For example, I have a pipeline stage that executes 3 jobs using the parallel command. When the 3 jobs are first executed, the pipeline stage status will be "In Progress". If the first job completes successfully, the pipeline stage status will change to "SUCCESS". This is despite the fact that the other 2 jobs are still running and "In Progress".
Correct behavior would be to have the pipeline stage status not change from "In Progress" until all the parallel jobs complete.