no Jenkins CI status info is published to/in gitlab

Summary

We have a GitLab/Jenkins setup. Jenkins will be triggered via webhook (our setup is like here ). This works pretty we, but i have updated to the lastest version (8.12 CE), and know no info from jenkins is visible. There is no build entry in the pipeline tab, there is no CI build .... above the accept merge request in a merge request.
We don't want to use GitLab CI at the moment (planned for the future).
This problem deactivate our hole existing CI pipeline 😨

Steps to reproduce

Create a setup like here. Make any push/merge request.

Expected behavior

Builds are available under the pipeline tab.

Actual behavior

NO Builds are available under the pipeline tab.

Relevant logs and/or screenshots

Output of checks

Results of GitLab application Check

everything is ok

Results of GitLab environment info

System information
System:         Ubuntu 14.04
Current User:   git
Using RVM:      no
Ruby Version:   2.3.1p112
Gem Version:    2.6.6
Bundler Version:1.13.1
Rake Version:   10.5.0
Sidekiq Version:4.1.4

GitLab information
Version:        8.12.0
Revision:       0864ff9
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            http://gitlab
HTTP Clone URL: http://gitlab/some-group/some-project.git
SSH Clone URL:  git@zkwgitlab:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no

GitLab Shell
Version:        3.6.0
Repository storage paths:
- default:      /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:            /opt/gitlab/embedded/bin/git

Possible fixes

I don't know how older version of GitLab checked that there is a running build only based on the webhook info, so it could be possible that newer version of GitLab want create a CI build if it is triggered via webhook.