[EFFx]

Use a boolean and set it true when the round ends and false when round starts. Check if the boolean is already true when doing ++1. It can help avoiding the twice increasement.
I've seen a lot of team swap codes, most of them are inside Furien Mod and all of them uses set_task to swap players teams. I've seen players had this issue before too, so this is what I have on mine, may help you with more efficiency instead of doing tricky ways:

PHP Code:

#include <amxmodx>
#include <cstrike>

#define PLUGIN "New Plug-In"
#define VERSION "1.0"
#define AUTHOR "author"

new g_iWins[2]

new pCvarMinCTWins
new pCvarMinTWins

public plugin_init() 
{
    register_plugin(PLUGIN, VERSION, AUTHOR)
    
    pCvarMinCTWins = register_cvar("minct_wins", "5")
    pCvarMinTWins = register_cvar("mint_wins", "5")
    
    register_logevent( "round_restart_event",   2, "0=World triggered", "1&Restart_Round_" )
    
    register_event("SendAudio", "EVENT_TWin", "a", "2&%!MRAD_terwin")
    register_event("SendAudio", "EVENT_CTWin", "a", "1=0", "2=%!MRAD_ctwin");
}

public round_restart_event()
{
    g_iWins[0] = g_iWins[1] = 0
}

public EVENT_CTWin() 
{
    g_iWins[1]++
    if(g_iWins[1] >= get_pcvar_num(pCvarMinCTWins))
    {
        g_iWins[1] = 0
        swapTeams()
    }
}

public EVENT_TWin() 
{
    g_iWins[0]++
    if(g_iWins[0] >= get_pcvar_num(pCvarMinTWins))
    {
        g_iWins[0] = 0
        swapTeams()
    }
}

swapTeams()
{
    new Players[32], PlayersNum, id;
    get_players(Players, PlayersNum, "h")
    if(PlayersNum) 
    {
        for(new i; i < PlayersNum; i++) 
        {
            id = Players[i]
            BeginDelay(id)
        }
    }
}

public BeginDelay(id) 
{
    if(is_user_connected(id)) 
    {
        switch(id) 
        {
            case 1..7: set_task(0.1, "BeginTeamSwap", id)
            case 8..15: set_task(0.2, "BeginTeamSwap", id)
            case 16..23: set_task(0.3, "BeginTeamSwap", id)
            case 24..32: set_task(0.4, "BeginTeamSwap", id)
        }
    }
}

public BeginTeamSwap(id) 
{
    if(is_user_connected(id)) 
    {
        switch(get_user_team(id)) 
        {
            case 1: cs_set_user_team(id, CS_TEAM_CT)
            case 2: cs_set_user_team(id, CS_TEAM_T)
        }
    }
}