Relation between issues and relation between MRs
We have already two reports about relations between issues (see also, depends, blocks, etc.) not being available. Although alternatives are available (you can read our expected workflow at https://wiki.gnome.org/Initiatives/DevelopmentInfrastructure/GitLabWorkflows#Maintainers_.26_developers) it's true that is a topic people raised through the process and feedback period and a topic we have raised to GitLab since the start.
Unfortunately this is in the enterprise edition and so far they are not pondering moving it to community edition. Let's keep this bug as a tracker of the status of this and other bug reports filed about this. GitLab CE issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/4058