Lose value of $uid_set

Server NGINX
1

Hello, master of nginx, I have a question when using
ngx_http_userid_module. here is the detail description:

nginx version:1.7
conf:

log_format main ‘$remote_addr - $remote_user [$time_local] “$request”
$uid_set’
…

server {

    userid on;

    userid_name user_id;

    set $uid_reset myuid;

       ...

}

because i set $uid_reset not empty, $uid_set would get a new uuid every
time nginx process a request.

but i found some strange things, I got value “-” of $uid_set, that means
$uid_set did not get a value. even though over 92% request have correct
value of $uid_set, but the 2% do not. And i did not found abnormal of
those
request.

Do you have any idea about this?

looking forward your reply!

have a nice day!

2

What is the http status code of those failed requests?

3

most of them is 301, status 200 is about 10% of status 301, and there
are
some other status. i can not find obvious regulation for them.

4

Is there some mistake ignored by me? I do not found useful information
for
this question, I am hoping you can give me some advises. maybe i should
try third module if this issue can not resolve。