I got the same error and it seems to be a problem with the gitlab api. My gitlab-log throws a 404 when trying to access a project bei namespace. I also tried to connect envoyer.io to gitlab with two brand new instances of gitlab and I'm having the same issues.
Here some github issues about this api-issue: https://github.com/gitlabhq/gitlabhq/issues/4921 https://github.com/gitlabhq/gitlabhq/issues/8290 https://github.com/gitlabhq/gitlabhq/issues/6954