There's definitely a sidebar on both, but they're not "connected" - the moderators need to set up the sidebar on the new site separately, and updates on either

There's definitely a sidebar on both, but they're not "connected" - the moderators need to set up the sidebar on the new site separately, and updates on either side don't affect the other one. A lot of subreddits just haven't bothered doing any setup on the new site (or don't even realize it's necessary).