plugin does not work with (multibranch) pipeline projects?

[Flow86]

In the log, I get this:

INFORMATION: gitlab web hook triggered for
   - group/repo url: ssh://git@repo-host/group/repo.git
   - branch: master
   - with payload:
{
  "object_kind": "push",
  "event_name": "push",
  "before": "651522384df8f144ffaaa367578ad5cd6f090443",
  "after": "17c5c6e90b1b2822e062b87d9ea029281221bf21",
  "ref": "refs/heads/master",
  "checkout_sha": "17c5c6e90b1b2822e062b87d9ea029281221bf21",
  "message": null,
  "user_id": 2,
  "project_id": 23,
  "project": {
    "name": "repo",
    "description": null,
    "web_url": "https://repo-host/group/repo",
    "avatar_url": null,
    "git_ssh_url": "ssh://git@repo-host/group/repo.git",
    "git_http_url": "https://repo-host/group/repo.git",
    "namespace": "rttr",
    "visibility_level": 0,
    "path_with_namespace": "group/repo",
    "default_branch": "master",
    "homepage": "https://repo-host/group/repo",
    "url": "ssh://git@repo-host/group/repo.git",
    "ssh_url": "ssh://git@repo-host/group/repo.git",
    "http_url": "https://repo-host/group/repo.git"
  },
  "commits": [
    {
      "id": "17c5c6e90b1b2822e062b87d9ea029281221bf21",
      "message": "mailer needs node\n",
      "timestamp": "2016-09-03T23:25:32+02:00",
      "url": "https://repo-host/group/repo/commit/17c5c6e90b1b2822e062b87d9ea029281221bf21",
      "added": [

      ],
      "modified": [
        "Jenkinsfile"
      ],
      "removed": [

      ]
    },
    {
      "id": "31c9eeb7af4094e66051c3303cc4add360febb61",
      "message": "add email notification\n",
      "timestamp": "2016-09-03T23:24:15+02:00",
      "url": "https://repo-host/group/repo/commit/31c9eeb7af4094e66051c3303cc4add360febb61",
      "added": [

      ],
      "modified": [
        "Jenkinsfile"
      ],
      "removed": [

      ]
    },
    {
      "id": "651522384df8f144ffaaa367578ad5cd6f090443",
      "timestamp": "2016-08-29T07:30:04+02:00",
      "url": "https://repo-host/group/repo/commit/651522384df8f144ffaaa367578ad5cd6f090443",
      "author": {
      },
      "added": [

      ],
      "modified": [
      ],
      "removed": [

      ]
    }
  ],
  "total_commits_count": 3,
  "repository": {
    "name": "repo",
    "url": "ssh://git@repo-host/group/repo.git",
    "description": null,
    "homepage": "https://repo-host/group/repo",
    "git_http_url": "https://repo-host/group/repo.git",
    "git_ssh_url": "ssh://git@repo-host/group/repo.git",
    "visibility_level": 0
  }
}
Sep 03, 2016 11:39:09 PM org.jruby.javasupport.JavaMethod invokeDirectWithExceptionHandling
INFORMATION: matching projects:
Sep 03, 2016 11:39:09 PM org.jruby.javasupport.JavaMethod invokeDirectWithExceptionHandling
WARNUNG: no project references the given group/repo url and commit branch

the git-url set in the project is "ssh://git@repo-host/group/repo.git" so I dont know why it does not work?