TFS 1.X+ Tfs 1.3 8.6 default source, bug in online players, after some time (rare bug)

[roriscrave]

hello, I'm using tfs 1.3 8.6 and there is a bug that happens rare (very rare)
there are 50 players playing and the site shows 50 for several days (ok).

but out of nowhere, someday, there are for example 50 players online and the site shows 40.
function website that count players online:

function user_count_online() {
    $online = mysql_select_single("SELECT COUNT(`player_id`) AS `value` FROM `players_online`;");
    return ($online !== false) ? $online['value'] : 0;
}

the function is correct, the error is that the site in players_online, sometimes shows the wrong number.
has 50 online, but the players_online table, for some reason bugs and shows only 40

the error could then be in the source, in this function (remembering that the bug is very rare, it happens about 1 time every 10 or 15 days).
edit: I have the impression that bug when the site receives some attack Ddos, wich website down or stay very slow. Could this be it or am I wrong?

void IOLoginData::updateOnlineStatus(uint32_t guid, bool login)
{
    if (g_config.getBoolean(ConfigManager::ALLOW_CLONES)) {
        return;
    }

    std::ostringstream query;
    if (login) {
        query << "INSERT INTO `players_online` VALUES (" << guid << ')';
    } else {
        query << "DELETE FROM `players_online` WHERE `player_id` = " << guid;
    }
    Database::getInstance().executeQuery(query.str());
}