Will offer my way of fixing.. probably something went wrong in the themes, aside from css, probably version mismatches with the core nodebb version your using. The below will revert to working vanilla and lavender theme versions that match w/ your core nodebb install version. (probably need to stick with whatever theme versions it reinstalls, because I've always had problems w/ updating themes, I don't upgrade them anymore) Stick with what came with the nodebb install originally. This will revert back to originals:
Yeah it might make more sense to use slugs instead of the actual group name when storing the key. Right now when you go to the group page you use a slug in the url and then the code grabs the group name using that slug to load the correct group's data.