Why is nginx unavailable during reload?

Question

Nginx

During the reload of the nginx config (4 cores, 4Gb, acts as a reverse proxy) temporarily stops responding to requests, including those that come to localhost (zabbix reports unavailability). RPS at the same time is at the level of 1600-1800, netstat does not show anything, in my opinion, unusual.

$ netstat -tpn |awk '/:80/||/:443/{print $6}' |sort |uniq -c                                                                    3 CLOSE_WAIT
     13 CLOSING
  17568 ESTABLISHED
    292 FIN_WAIT1
    962 FIN_WAIT2
    171 LAST_ACK
    309 SYN_RECV
  54314 TIME_WAIT

$ netstat -tpn |awk '/nginx/{print $6,$7}' |sort |uniq -c
   3124 ESTABLISHED 10005/nginx
   3073 ESTABLISHED 10006/nginx
   2965 ESTABLISHED 10007/nginx
   2980 ESTABLISHED 10008/nginx

some nginx.conf:

worker_processes  4;
timer_resolution 100ms;
worker_priority -15;
worker_rlimit_nofile 200000;

events {
  worker_connections  65536;
  multi_accept on;
  use epoll;
}

http {

  sendfile on;
  tcp_nopush on;
  tcp_nodelay on;

  keepalive_requests 100;
  keepalive_timeout  65;

  server {
    listen  80 default_server backlog=1000;
    listen  443 ssl backlog=1000;
    ....
    }
}

custom sysctl.conf

net.ipv4.ip_local_port_range=1024 65535
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.all.secure_redirects=0
net.ipv4.conf.all.send_redirects=0
net.core.netdev_max_backlog=10000
net.ipv4.tcp_syncookies=0
net.ipv4.tcp_max_syn_backlog=20480
net.ipv4.tcp_synack_retries=2
net.ipv4.tcp_syn_retries=2
net.ipv4.tcp_rmem=4096 87380 16777216
net.ipv4.tcp_wmem=4096 65536 16777216
net.core.rmem_max=16777216
net.core.wmem_max=16777216
net.netfilter.nf_conntrack_max=1048576
net.ipv4.tcp_congestion_control=htcp
net.ipv4.tcp_timestamps=1
net.ipv4.tcp_no_metrics_save=1
net.ipv4.tcp_tw_reuse=1
net.ipv4.tcp_tw_recycle=0
net.ipv4.tcp_max_tw_buckets=1400000
net.core.somaxconn=250000
net.ipv4.tcp_keepalive_time=900
net.ipv4.tcp_keepalive_intvl=15
net.ipv4.tcp_keepalive_probes=5
net.ipv4.tcp_fin_timeout=10

Answer 1

dmesg+error.log?
+ useful to add tcp charts to zabbix from netstat -s

Answer 2

There is exactly the same problem. Also, nginx stops responding when the logs are rotated.
The reason could not be found.