i think there is definitely some kind of permissions issue with the new groups.
i had myself as super admin (still super admin) and my colleagues as executive, and their personal settings were at 0, ie, for each individual they had no permissions for anything. they are all part of a group, that has full permissions for workspaces, full for users and limited for other admin stuff. once i changed their user type to manager (instead of executive), with same user perms, and group perms, i can assign tasks to them.
i dont know if this is on purpose, but seems weird that user type trumps other permissions, for example, if a user is set to executive, but i give them additional custom permissions in a group, they should get those. that way i dont have to change user type when i change permissions, just use the group setting for mass changes, and user type stays the same, so i dont have to explain why employee x is set to manager, but employee y is set to executive.