Running Jenkins Workflow version 1.10, I have noticed that sometimes the Build queue will show jobs queued with a display name of part of unknown step, or an executor will be executing something called Unknown Task
These tasks can't be cancelled. I'm curious what these unknown tasks / steps signify and how a workflow step gets into this state and finally if they can be prevented. I did try searching the Internet and the workflow plugin documentation, but I couldn't find an answer.
It means there is a bug. 1.11 makes it possible to cancel these when they occur. The root causes continue to be investigated as they are reproduced.