This occurs occasionally on ci.jenkins.io with the default buildPlugin() pipeline from https://github.com/jenkins-infra/pipeline-library
The Linux agent is available quickly, the Windows agent takes forever to come online.
Blue Ocean tells me for quite a long time that it's waiting for the windows agent… when the Linux build in the paralle() step is already finished. Knowing this would be very useful information.
Screen shots attached. Times are off 2 hours due to my time zone, but it shows clearly one parallel is done, but BO doesn't tell me.