I agree, we're using gitlab too and the only problem is the lack of ticket system feature (due date/alert reminder, multiple people assignment, advanced filters, simple markdown text editor for client, time tracking, edit default label for all project,...) otherwise we hightly recommend it.
Thanks, we're looking some of these but we want to keep it light and easy to use at the same time. Please be aware that some scrum tools also integrate with GitLab https://about.gitlab.com/applications/#scrum-boards