[error] 2542506#2542506: *333780 recv() failed (104: Unknown error) while reading response header fr

Facing this issue from last few weeks repeatedly. but Memory and CPU usage are still under the thresold limit of 90%. also facing frequent Deadlocks.
added few configuration added to solve issue
proxy_connect_timeout 900s;
proxy_send_timeout 900s;
proxy_read_timeout 900s;