Peer closed connection in SSL handshake

I have a question about nginx. I created a reverse proxy by nginx. Activated SSL encryption with Letsencrypt. All is ok and all requests from client are sent to origin server specified in upstream. Sometimes I have error > 502 Bad Gateway nginx/1.16.1 in chrome browser. Checked nginx error.log and this is the error: > peer closed connection in SSL handshake 104: Connection reset by peer while SSL handshaking to upstream. I searched and tested all suggestions. Still sometimes this error occurs. example.com.conf: upstream example_com { server 50.90.20.70:443 max_fails=10 fail_timeout=60s; } server { server_name *.example_com; location / { #proxy_ssl_server_name on; proxy_pass https://example_com ; proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504; proxy_set_header Accept-Encoding ""; proxy_set_header Host "example.com"; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; add_header Front-End-Https on; add_header 'host' "$host"; add_header Strict-Transport-Security "max-age=31536000"; proxy_redirect off; proxy_buffering on; proxy_cache off; proxy_cache_valid 200 4h; proxy_cache_use_stale error timeout invalid_header updating http_500 http_502 http_503 http_504; #proxy_ssl_verify on; #proxy_ssl_trusted_certificate /etc/letsencrypt/live/example.com/fullchain.pem; proxy_ssl_server_name on; proxy_ssl_session_reuse off; } listen 443 ssl; ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; include /etc/letsencrypt/options-ssl-nginx.conf; ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; #ssl_ecdh_curve secp384r1:prime256v1; } server { if ($host = example.com) { return 301 https://$host$request_uri ; } server_name example.com; listen 80; return 404; } nginx.conf: user nginx; worker_processes 6; worker_rlimit_nofile 5000; error_log /var/log/nginx/error.log warn; pid /var/run/nginx.pid; events { worker_connections 1000; multi_accept on; } http { include /etc/nginx/mime.types; default_type application/octet-stream; proxy_cache_path /etc/nginx/cache levels=1:2 keys_zone=STATIC:10m inactive=1h max_size=950g; log_format main '$host' access_log /var/log/nginx/access.log main; sendfile off; tcp_nopush on; #server_names_hash_max_size: 512; server_names_hash_bucket_size 128; keepalive_timeout 65; large_client_header_buffers 4 32k; client_max_body_size 100M; proxy_no_cache $cookie_nocache $arg_nocache$arg_comment $http_x_no_cache; proxy_no_cache $http_pragma $http_authorization; proxy_cache_bypass $cookie_nocache $arg_nocache $arg_comment; proxy_cache_bypass $http_pragma $http_authorization $http_x_no_cache ; proxy_ssl_server_name on; #gzip on; gzip on; gzip_buffers 16 8k; gzip_comp_level 6; gzip_http_version 1.1; gzip_min_length 256; gzip_proxied any; gzip_vary on; gzip_types text/xml application/xml application/atom+xml application/rss+xml applicati$ text/javascript application/javascript application/x-javascript text/x-json application/json application/x-web-app-manifest+json text/css text/plain text/x-component font/opentype application/x-font-ttf application/vnd.ms-fontobject image/x-icon; gzip_disable "MSIE [1-6]\.(?!.*SV1)"; # include /etc/nginx/conf.d/*.conf; server { error_page 500 502 503 504 /error503.html; location = /error503.html { root /usr/share/nginx/html; internal; } } include /etc/nginx/conf.d/*.conf; }