I have seen one possible issue in your code, keep in mind not tested. When printing your final result, you check the members count if more than 1 instead of 0 (the Members List should not contain the creator of the team).

 
                if (team.Members.Count > 0)
                {
                    Console.WriteLine($"{team.TeamName}");
                    Console.WriteLine($"- {team.Creator}");
                    for (int i = 1; i < team.Members.Count; i++)
                    {
                        Console.WriteLine($"-- {team.Members[i]}");
                    }
 
                }

Demo code =>

using System;
using System.Linq;
using System.Collections.Generic;

namespace teamworkProject
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            List<Team> teamList = new List<Team>();

            for (int i = 0; i < n; i++)
            {
                string[] teamCreator = Console.ReadLine().Split('-');
                string creator = teamCreator[0];
                string teamName = teamCreator[1];
                TeamCreator(teamList, creator, teamName);

            }

            string memberInput = Console.ReadLine();
            while (memberInput != "end of assignment")
            {
                string[] memberSplit = memberInput.Split("->");
                string member = memberSplit[0];
                string teamName = memberSplit[1];
                bool creatorCheck = CreatorCheck(member, teamName, teamList);
                if (creatorCheck == false)
                {
                    MemberCreator(teamList, member, teamName);
                }
                memberInput = Console.ReadLine();
            }

            teamList = teamList.OrderByDescending(x => x.Members.Count).ThenBy(x => x.TeamName).ToList();
            foreach (var team in teamList)
            {
                team.Members.Sort();
            }
            TeamPrinter(teamList);

            List<Team> noMemberTeams = new List<Team>();
            NoMemberPrinter(noMemberTeams, teamList);

        }

        static bool CreatorCheck(string member,string teamName, List<Team> teamList)
        {
            bool creatorCheck = false;

            foreach (var team in teamList)
            {
                if (team.Creator == member && team.TeamName == teamName)
                {
                    Console.WriteLine($"Member {member} cannot join team {team.TeamName}!");
                    creatorCheck = true;
                    return creatorCheck;
                }
                else if (team.Creator == member && team.TeamName != teamName)
                {
                    Console.WriteLine($"{member} cannot create another team!");
                    creatorCheck = true;
                    return creatorCheck;
                }
            }

            return creatorCheck;
        }

        static void NoMemberPrinter(List<Team> noMemberTeams, List<Team> teamList)
        {
            foreach (var team in teamList)
            {
                if (team.Members.Count == 0)
                {
                    Team newTeam = new Team(team.Creator, team.TeamName);
                    noMemberTeams.Add(newTeam);
                }
            }
            noMemberTeams = noMemberTeams.OrderBy(x => x.TeamName).ToList();
            Console.WriteLine("Teams to disband:");
            foreach (var team in noMemberTeams)
            {
                Console.WriteLine($"{team.TeamName}");
            }

        }

        static void TeamPrinter(List<Team> teamList)
        {
            foreach (var team in teamList)
            {
                if (team.Members.Count > 0)
                {
                    Console.WriteLine($"{team.TeamName}");
                    Console.WriteLine($"- {team.Creator}");
                    foreach (var person in team.Members)
                    {
                        Console.WriteLine($"-- {person}");
                    }
                }
            }
        }

        static List<Team> MemberCreator(List<Team> teamList, string member, string teamName)
        {
            bool teamFail = true;
            bool memberFail = false;
            foreach (var team in teamList)
            {
                if (team.TeamName == teamName)
                {
                    teamFail = false;
                }
            }
            if (teamFail)
            {
                Console.WriteLine($"Team {teamName} does not exist!");
                return teamList;
            }

            foreach (var team in teamList)
            {
                foreach (var person in team.Members)
                {
                    if (person == member)
                    {
                        memberFail = true;
                    }
                }
            }
            if (memberFail)
            {
                Console.WriteLine($"Member {member} cannot join team {teamName}!");
                return teamList;
            }

            foreach (var team in teamList)
            {
                if (team.TeamName == teamName)
                {
                    team.Members.Add(member);
                    break;
                }
            }

            return teamList;
        }


        static List<Team> TeamCreator(List<Team> teamList, string creator, string teamName)
        {
            foreach (var team in teamList)
            {
                if (teamName == team.TeamName)
                {
                    Console.WriteLine($"Team {teamName} was already created!");
                    return teamList;
                }
            }

            foreach (var team in teamList)
            {
                if (creator == team.Creator)
                {
                    Console.WriteLine($"{creator} cannot create another team!");
                    return teamList;
                }
            }

            Team newTeam = new Team(creator, teamName);
            teamList.Add(newTeam);
            Console.WriteLine($"Team {teamName} has been created by {creator}!");
            return teamList;
        }
    }

    class Team
    {
        public string Creator { get; set; }

        public string TeamName { get; set; }

        public List<string> Members { get; set; }

        public Team(string creator, string teamName)
        {
            Creator = creator;
            TeamName = teamName;
            Members = new List<string>();
        }
    }
}

OK, i found my mistake, and its rly dumb one but.... "For each team, you have to print its members sorted by
name (ascending). " i didnt do that....

i did sort team by members.count and TeamName, but never sorted the members... and the time that consume.... atleast now i can give my mind a rest.

It's mine new code and as @ Axiomatik suggest i remove teamCreator from team.

if anyone is interested https://pastebin.com/8EywHagV .