The WorkflowGraph has a static class WorkflowGraphListener.FlowNodeContainer. This class contains a map that is populated with a Run object every time a new Flow Head is created! This hinder the normal garbage collection of Runs.
It may cause Jenkins to hang, in which case Jenkins needs to be restarted.
I have tested the simplest case scenario and run a simple pipeline that just just do:
Every time the run completes, the map size is increased by one. This never decreases. In large instances with lots of pipeline jobs, this is a problem...