то есть все таки мало кода?

а что тебя не устраивает?

import UIKit

class MainViewController: UITabBarController {
   
   private let profileViewController: ProfileViewController = {
       let vc = ProfileViewController()
       vc.tabBarItem.title = "Profile"
       return vc
   }()
   
   private let inviteFriendsViewController: InviteFriendsViewController = {
       let vc = InviteFriendsViewController()
       vc.tabBarItem.title = "Invite friend"
       return vc
   }()
   
   private let invitationsViewController: InvitationsViewController = {
       let vc = InvitationsViewController()
       vc.tabBarItem.title = "Invitations"
       return vc
   }()
   
   private let chatsViewController: ChatsViewController = {
       let vc = ChatsViewController()
       vc.tabBarItem.title = "Chats"
       return vc
   }()
   
   private let editGalleryViewController: EditGalleryViewController = {
       let vc = EditGalleryViewController()
       vc.tabBarItem.title = "Gallery"
       return vc
   }()
   
   private let editFieldNavController: EditGroupNavController = {
       let vc = EditGroupNavController()
       vc.tabBarItem.title = "Edit field"
       return vc
   }()
   
   private let editHiddenFieldNavController: EditGroupNavController = {
       let vc = EditGroupNavController()
       vc.tabBarItem.title = "Hidden field"
       return vc
   }()
   
   private let searchMemberViewController: SearchMemberViewController = {
       let vc = SearchMemberViewController()
       vc.tabBarItem.title = "Member"
       return vc
   }()
   
   private let supportViewController: SupportViewController = {
       let vc = SupportViewController()
       vc.tabBarItem.title = "Support"
       return vc
   }()
   
   private let moreController: UIViewController = {
       let vc = UIViewController()
       vc.tabBarItem.title = "More"
       return vc
   }()
   
   var networkManager: NetworkManagment?
   
   override func viewDidLoad() {
       super.viewDidLoad()
       
       let vc1 = EditGroupNavController()
       let vc2 = EditGalleryViewController()
       let vc3 = SearchMemberViewController()
       let vc4 = SupportViewController()
       let vc5 = InviteFriendsViewController()
       let vc6 = ChatsViewController()
       
       
       setupNetworkManager()
       setupNavigationBar()
       
//        viewControllers = [editFieldNavController, editGalleryViewController, searchMemberViewController, supportViewController, moreController, inviteFriendsViewController]
       viewControllers = [vc1, vc2, vc3, vc4, vc5, vc6]
       print(viewControllers)
       viewControllers?.append(vc5)
       print(viewControllers)
       viewControllers?.append(vc6)
       print(viewControllers)
   }
   
   private func setupNetworkManager() {
       let networking = NetworkService()
       networkManager = NetworkManager(networking: networking)
   }
   
   private func setupNavigationBar() {
       self.navigationController?.setNavigationBarHidden(true, animated: false)
       self.navigationItem.setHidesBackButton(true, animated: false)
   }
   
   override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {
       print(viewControllers)
   }
}

ты берешь и снова их суешь

import UIKit

class MainViewController: UITabBarController {
   
   private let profileViewController: ProfileViewController = {
       let vc = ProfileViewController()
       vc.tabBarItem.title = "Profile"
       return vc
   }()
   
   private let inviteFriendsViewController: InviteFriendsViewController = {
       let vc = InviteFriendsViewController()
       vc.tabBarItem.title = "Invite friend"
       return vc
   }()
   
   private let invitationsViewController: InvitationsViewController = {
       let vc = InvitationsViewController()
       vc.tabBarItem.title = "Invitations"
       return vc
   }()
   
   private let chatsViewController: ChatsViewController = {
       let vc = ChatsViewController()
       vc.tabBarItem.title = "Chats"
       return vc
   }()
   
   private let editGalleryViewController: EditGalleryViewController = {
       let vc = EditGalleryViewController()
       vc.tabBarItem.title = "Gallery"
       return vc
   }()
   
   private let editFieldNavController: EditGroupNavController = {
       let vc = EditGroupNavController()
       vc.tabBarItem.title = "Edit field"
       return vc
   }()
   
   private let editHiddenFieldNavController: EditGroupNavController = {
       let vc = EditGroupNavController()
       vc.tabBarItem.title = "Hidden field"
       return vc
   }()
   
   private let searchMemberViewController: SearchMemberViewController = {
       let vc = SearchMemberViewController()
       vc.tabBarItem.title = "Member"
       return vc
   }()
   
   private let supportViewController: SupportViewController = {
       let vc = SupportViewController()
       vc.tabBarItem.title = "Support"
       return vc
   }()
   
   private let moreController: UIViewController = {
       let vc = UIViewController()
       vc.tabBarItem.title = "More"
       return vc
   }()
   
   var networkManager: NetworkManagment?
   
   override func viewDidLoad() {
       super.viewDidLoad()
       
//        let vc1 = EditGroupNavController()
//        let vc2 = EditGalleryViewController()
//        let vc3 = SearchMemberViewController()
//        let vc4 = SupportViewController()
//        let vc5 = InviteFriendsViewController()
//        let vc6 = ChatsViewController()
       
       let vc1 = UIViewController()
       vc1.view.backgroundColor =  colorLiteral(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
       vc1.tabBarItem.title = "First"
       let vc2 = UIViewController()
       vc2.view.backgroundColor =  colorLiteral(red: 0.1019607857, green: 0.2784313858, blue: 0.400000006, alpha: 1)
       vc2.tabBarItem.title = "Second"
       let vc3 = UIViewController()
       vc3.view.backgroundColor =  colorLiteral(red: 0.1215686277, green: 0.01176470611, blue: 0.4235294163, alpha: 1)
       vc3.tabBarItem.title = "Third"
       let vc4 = UIViewController()
       vc4.view.backgroundColor =  colorLiteral(red: 0.4392156899, green: 0.01176470611, blue: 0.1921568662, alpha: 1)
       vc4.tabBarItem.title = "Fourth"
       let vc5 = UIViewController()
       vc5.view.backgroundColor =  colorLiteral(red: 0.9254902005, green: 0.2352941185, blue: 0.1019607857, alpha: 1)
       vc5.tabBarItem.title = "Fifth"
       let vc6 = UIViewController()
       vc6.view.backgroundColor =  colorLiteral(red: 0.9529411793, green: 0.6862745285, blue: 0.1333333403, alpha: 1)
       vc6.tabBarItem.title = "Sixth"
       
       
       setupNetworkManager()
       setupNavigationBar()
       
//        viewControllers = [editFieldNavController, editGalleryViewController, searchMemberViewController, supportViewController, moreController, inviteFriendsViewController]
       viewControllers = [vc1, vc2, vc3, vc4, vc5, vc6]
   }
   
   private func setupNetworkManager() {
       let networking = NetworkService()
       networkManager = NetworkManager(networking: networking)
   }
   
   private func setupNavigationBar() {
       self.navigationController?.setNavigationBarHidden(true, animated: false)

ты берешь и снова их суешь

я же в самом начале скинул скрин с принтом массива. Там забавно то, что ты инициализируешь массив 6 элементами принтуешь, а там 4!