When registering the webhooks at github. Regardless if using explicitly the "re-register"-button or indirectly while creating a multipipeline build the Webhooks for "Repository" and "Pull Requests" are set. Not set is the "Push" Webhook. This leads to the behaviour that pushes to github repositories aren't sent to jenkins. For that case I've got to use timebased polling which makes the whole webhook-thing useless. To get the pushes working I've got to activate the webhook manually. This works until I push the re-register button. Then they're gone.