KAS doesn't want to start, says unknown field "kubernetes_api"

Hey! I tried to enable KAS on my Gitlab CE Instance (installed via official Helm Chart). Everything seems to be configured correctly and the KAS pods are created. By they fail to start with following error on their console:

level=error msg="Program aborted" error="protojson.Unmarshal: proto: (line 1:11): unknown field \"kubernetes_api\""

Has anyone an idea what that could mean?