Can't upload a few files via nginx

[WusikiJeronii]

If I upload 1,2,10 files uploading works, but I tried to upload 37 files and
I get the error in the error.log:
> 2021/08/23 16:37:04 [error] 19943#19943: *1 sendfile() failed (32: Broken
pipe) while sending request to upstream, client: 127.0.0.1, server:
localhost, request: "POST /upload/project HTTP/1.1", upstream:
"http://127.0.0.1:8070/upload/project", host: "127.0.0.1", referrer:
"http://127.0.0.1/projects"

But if I try to upload these 37 files without Nginx uploading will be
successful.

I tried:

* client_max_body_size 10240m;
* keepalive_timeout 600;

Doesn't work.

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,292278,292278#msg-292278