GitLab CE taking over website, not working on subdomain

Hello,

I tried installing gitlab ce via the Omnibus package the on my server today,

While I seemed to run fine for a while I now noticed, that it does not work on my subdomain (e.g. gitlab.example.com) anymore, but it runs on example.com, my main domain, taking over all web content and redirecting all traffic to example.com/users/sign_in.

I checked my DNS records and they are definately pointing gitlab.example.com to my IP,
I have not changed the config after making sure it works (only external_url is uncommented)
I have made sure the external_url in /etc/gitlab/gitlab.rb points to http://gitlab.mydomain.com (in my case it’s
I have tried gitlab-ctl reconfigure and gitlab-ctl restart
Using Debian 8 Jessie

Thanks in advance for any tips.

Are you using the nginx webserver built in to the omnibus package or are you using another and proxying the requests?