I use a pipeline build triggered by github webhooks using the dynamic EC2 nodes (Amazon EC2 plugin).

"GitHub hook trigger for GITScm polling" is checked and I'm using "Additional Behaviors -> Polling ignores commits in certain paths".  When using dynamic EC2 agents, build is not triggered and I see the following message in the logs:

"no such computer EC2 (agent) - agent id"

EC2 agents are not provisioned and build will not start, this is a bug which affects a lot of teams in a production environment.