我有以下承诺链。通过查看记录器语句，我期望控制台显示：

'2. Getting room', '3. Getting spontaneous session', '3A. Getting spontaneous session', '4. Attaching to meeting', '4A. Attached to meeting',

但我得到的却是：

'2. Getting room', '3. Getting spontaneous session', '3A. Getting spontaneous session', '4A. Attached to meeting', '4. Attaching to meeting',

有人能解释一下为什么在第二个“then”返回任何内容之前就命中了第三个“then”吗？

logger.log('2. Getting room', 2, room);
RoomStore.getRoom(room, function(err, sessionIds) {
    let user = req.body.user;

    logger.log('2A. Getting room', 2, room);
    logger.log('3. Getting spontaneous session', 2, room);
    getSpontaneousZipdxSession(user, room).
    then(function(urls) {
        resolvedUrls = urls;
        logger.log('3A. Getting spontaneous session', 2, room);
        return connectTokboxZip(urls.url, sessionIds[0], room);
    }).
    then(function() {
        if (req.body.translated === 'true') {
            connectTokboxZip(resolvedUrls.englishSessionUrl, sessionIds[1], room).then(function() {
                logger.log('4. Attaching to meeting', 2, room);
                return attachToMeeting(user, room);
            });
        }
        else {
            logger.log('4. Attaching to meeting', 2, room);
            return attachToMeeting(user, room);
        }
    }).
    then(function() {
        logger.log('4A. Attached to meeting', 2, room);
        logger.log('Connecting room to zipdx SUCCESS!', 2, room);
        communications.sendZipDxConnectedMessage(room);
        resp.sendStatus(200);
    }).
    catch(function(error) {
        logger.log('Connecting room to zipdx failed: ' + error, 2, room);
        resp.statusMessage = error;
        resp.status(500).end();
    });
});