On master the group title setting has moved from the settings page to the profile edit page. In the database the groupTitle property is in the user hash(user:1) now instead of the user settings hash(user:1:settings).
Relevant commits
https://github.com/NodeBB/NodeBB/commit/e564260650b5ed5191fde1c464fa87c68b3ce78f
If you have a custom theme that has a custom edit/settings page you can apply this change
https://github.com/NodeBB/nodebb-theme-vanilla/commit/68f6975c404af2b72a937c77659c7d2fec7e116b