[Effeff]

Suggested changes:

• Respawn players later. You are currently respawning the players before they are placed on a team.
  
• Check if the team change was successful. A side effect of using "jointeam" is that the command does not place players on a team if the team is full. A team is full when there are not enough spawn points available.

ChangeClientTeam does not care if there are enough spawnpoints available. It will just spawn the player inside of a teammate. An additional check would be required in this case - mp_solid_teammates. I am uncertain if there are other side effects to using ChangeClientTeam instead of the ClientCommand like you have been doing, so I have not included this in the snippet below. Instead, I just LogError and move the player from the unassigned team to spectator.

PHP Code:

#include <cstrike>
#include <sdktools>

ConVar g_ConVar_GraceTime;

bool g_bSpawnAllowed = true;
bool g_bJoinTeamAllowed[MAXPLAYERS +1];

public Plugin myinfo =  {
    name = "[CSGO] Auto Team Assign", 
    author = "SM9();", 
    description = "Assigns a team automatically when player connects and bypasses team menu", 
    version = "1.0.3", 
    url = "https://sm9.dev"
};

public void OnPluginStart() {
    HookEvent("round_start", Event_RoundStart);
    HookEvent("round_end", Event_RoundEnd);
    HookEvent("player_connect_full", Event_PlayerConnectFull);

    AddCommandListener(CommandListener_JoinTeam, "jointeam");
    
    g_ConVar_GraceTime = FindConVar("mp_join_grace_time");
}

public void OnMapStart() {
    g_bSpawnAllowed = true;
}

Action CommandListener_JoinTeam(int client, const char[] command, int args) {
    if (g_bJoinTeamAllowed[client]) {
        g_bJoinTeamAllowed[client] = false;
        RequestFrame(Frame_CheckClientTeam, GetClientUserId(client));
        return Plugin_Continue;
    }
    return Plugin_Handled;
}

void Frame_CheckClientTeam(int userid) {
    int client = GetClientOfUserId(userid);
    if (!client) {
        return;
    }
    int team = GetClientTeam(client);
    if (team == CS_TEAM_NONE) {
        ChangeClientTeam(client, CS_TEAM_SPECTATOR);
        LogError("Failed to assign client to a team because the map does not have enough spawnpoints");
        return;
    }
    if (!IsPlayerAlive(client) && team > CS_TEAM_SPECTATOR && (g_bSpawnAllowed || areTeamsEmpty())) {
        CS_RespawnPlayer(client);
    }
}

void Event_PlayerConnectFull(Event event, const char[] name, bool dontBroadcast) {
    int client = GetClientOfUserId(event.GetInt("userid"));
    g_bJoinTeamAllowed[client] = true;
    ClientCommand(client, "jointeam 0 %i", determineTeam());
}

void Event_RoundStart(Event event, char[] name, bool dontBroadcast) {
    bool warmupActive = isWarmupActive();
    
    if (warmupActive || g_ConVar_GraceTime.BoolValue) {
        g_bSpawnAllowed = true;
    }
    
    if (warmupActive) {
        return;
    }
    
    CreateTimer(g_ConVar_GraceTime.FloatValue, Timer_GraceTimeOver, _, TIMER_FLAG_NO_MAPCHANGE);
}

void Event_RoundEnd(Event event, char[] name, bool dontBroadcast) {
    g_bSpawnAllowed = false;
}

Action Timer_GraceTimeOver(Handle timer) {
    g_bSpawnAllowed = false;
}

public void OnClientDisconnect(int client) {
    g_bJoinTeamAllowed[client] = false;

    if (!areTeamsEmpty()) {
        return;
    }
    
    g_bSpawnAllowed = true;
}

bool isWarmupActive() {
    return view_as<bool>(GameRules_GetProp("m_bWarmupPeriod"));
}

bool areTeamsEmpty() {
    return !(GetTeamClientCount(CS_TEAM_T) + GetTeamClientCount(CS_TEAM_CT));
}

int determineTeam() {
    int tCount = GetTeamClientCount(CS_TEAM_T);
    int ctCount = GetTeamClientCount(CS_TEAM_CT);
    
    return tCount == ctCount ? GetRandomInt(CS_TEAM_T, CS_TEAM_CT) : tCount < ctCount ? CS_TEAM_T : CS_TEAM_CT;
}