Having rare ERR_SSL_PROTOCOL_ERROR error in browser while using own proxy with haproxy routing all on the server in one port. Can get error on randome websites 1+ time a day, and reloading page fix it. Before using haproxy there was no errors like this. My haproxy.cfg looks like this:

   log /dev/log	local0
   log /dev/log	local1 notice
   chroot /var/lib/haproxy
   stats socket /run/haproxy/admin.sock mode 660 level admin expose-fd listeners
   stats timeout 30s
   user haproxy
   group haproxy

   # Default SSL material locations
   ca-base /etc/ssl/certs
   crt-base /etc/ssl/private

   # See:
       ssl-default-bind-ciphersuites TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
       ssl-default-bind-options ssl-min-ver TLSv1.2 no-tls-tickets

   log	global
   mode	http
   option	httplog
   option	dontlognull
       timeout connect 5000
       timeout client  50000
       timeout server  50000
   errorfile 400 /etc/haproxy/errors/400.http
   errorfile 403 /etc/haproxy/errors/403.http
   errorfile 408 /etc/haproxy/errors/408.http
   errorfile 500 /etc/haproxy/errors/500.http
   errorfile 502 /etc/haproxy/errors/502.http
   errorfile 503 /etc/haproxy/errors/503.http
   errorfile 504 /etc/haproxy/errors/504.http

listen front
   mode tcp
   bind *:443

   tcp-request inspect-delay 5s
   tcp-request content accept if { req_ssl_hello_type 1 }

   use_backend dns if { req.ssl_sni -m end dns.domain }
   use_backend panel if { req.ssl_sni -m end panel.domain }
   use_backend reality if { req.ssl_sni -m end }
   default_backend fallback

backend dns
   mode tcp
   server adguard

backend panel
   mode tcp
   server srv1

backend fallback
   mode tcp
   server srv1

backend reality
   mode tcp
   server srv1 send-proxy

Update: from logs I found this

SD 20/20/19/19/0 0/0 - SD indicates about connection error.