Вот еще такое встречается крайне редко в логе nginx ;
2017/12/27 12:02:55 [info] 9116#101634: *202092 setsockopt(TCP_NODELAY) failed (54: Connection reset by peer) while keepalive, client: 127.0.0.1, server: 0.0.0.0:80


При этом:
collectd
[2017-12-27 12:02:55] [warning] nginx plugin: curl_easy_perform failed: Operation timed out after 10001 milliseconds with 0 bytes received
[2017-12-27 12:02:55] [notice] read-function of plugin `nginx' failed. Will suspend it for 80.000 seconds.

tcpdump:
12:02:54.813317 IP 127.0.0.1.19117 > 127.0.0.1.80: Flags [F.], seq 91, ack 1, win 1275, options [nop,nop,TS val 30902236 ecr 737003093], length 0
12:02:54.813324 IP 127.0.0.1.80 > 127.0.0.1.19117: Flags [.], ack 92, win 1274, options [nop,nop,TS val 737012990 ecr 30902236], length 0
12:02:55.486115 IP 127.0.0.1.80 > 127.0.0.1.18902: Flags [P.], seq 1:261, ack 92, win 1275, options [nop,nop,TS val 2230401244 ecr 30862237], length 260
12:02:55.757720 IP 127.0.0.1.80 > 127.0.0.1.18902: Flags [F.], seq 261, ack 92, win 1275, options [nop,nop,TS val 2230401516 ecr 30862237], length 0
12:02:55.810233 IP 127.0.0.1.80 > 127.0.0.1.18902: Flags [FP.], seq 1:261, ack 92, win 1275, options [nop,nop,TS val 2230401569 ecr 30862237], length 260
12:02:55.844458 IP 127.0.0.1.80 > 127.0.0.1.19117: Flags [P.], seq 1:260, ack 92, win 1275, options [nop,nop,TS val 737014021 ecr 30902236], length 259
12:02:55.844471 IP 127.0.0.1.19117 > 127.0.0.1.80: Flags [R], seq 1783156127, win 0, length 0
12:02:56.258235 IP 127.0.0.1.80 > 127.0.0.1.18902: Flags [FP.], seq 1:261, ack 92, win 1275, options [nop,nop,TS val 2230402017 ecr 30862237], length 260