Log Analytics: "invalid log lines" on HTTP 408 - help with regex

I’m running Log Analytics cron job daily.
And I noticed, that one my site always have few invalid log lines:

    23183 requests imported successfully
    10 requests were downloads
    1294 requests ignored:
        0 HTTP errors
        20 HTTP redirects
        501 invalid log lines
        0 requests did not match any known site
        0 requests did not match any --hostname
        8 requests done by bots, search engines...
        765 requests to static resources (css, js, images, ico, ttf...)

While investigating (I ran the job with --debug --debug), I found, that invalid log lines are ones, with HTTP 408 status:
2017-09-30 19:31:53,110: [DEBUG] Invalid line detected (line did not match): - - [29/Sep/2017:15:54:22 -0700] "-" 408 3187 "-" "-" 21

Normal log line looks like this: - - [22/Sep/2017:00:46:34 -0700] "GET /index.php/res/Ghost.nwc?dir=start HTTP/1.1" 200 10052 "-" "Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)" 3383

These all are valid Apache log lines. This is my Apache log format:
LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\" %D" timed

So, I think the issue is caused by my --log-format-regex option. Can I get help on how can I fix it? Here is my current format setting for the option:
FORMAT="(?P<ip>\S+) \S+ \S+ \[(?P<date>.*?) (?P<timezone>.*?)\] \"\S+ (?P<path>.*?) \S+\" (?P<status>\S+) (?P<length>\S+) \"(?P<referrer>.*?)\" \"(?P<user_agent>.*?)\" (?P<generation_time_micro>\S+)"

python /var/www/html/misc/log-analytics/import_logs.py \
    --url=$PIWIK --recorders=2 --enable-http-errors \
    --idsite=4 $LOCATION \