Haproxy freez and too many wating connection to the upstreams

Help!
1

hello everybody
I have set up a HAproxy to handel about 100K rps and then proxied that to the 4 nginx
but suddenly all the connection from HAproxy to the nginxes become
connection wating (red line) and the connection established (blue line) become minimum and all the cpu’s that allocated to the haproxy become 100%
this is the HAproxy configuration :

global 
    nbproc 1
    nbthread 8
    cpu-map auto:1/1-8 0-7
    maxconn 500000
    ...
defaults
    timeout connect 7s
    timeout client  14s
    timeout server  14s
    ...
frontend https_in
    maxconn 500000
    mode tcp
    ...

and here is the kernel configuration:

net.ipv4.ip_forward=1
net.ipv4.ip_nonlocal_bind = 1
fs.file-max = 10000000
fs.nr_open = 10000000
net.ipv4.ip_local_port_range = 1024 65535
net.ipv4.tcp_max_syn_backlog = 65536
net.core.somaxconn = 65535
net.core.netdev_max_backlog = 65536
net.ipv4.tcp_max_orphans = 262144

and also keepalive timeout in nginxes are 30s

HAproxy Vevrsion : HA-Proxy version 2.3.10-1ppa1~focal 2021/04/24
OS Version : Ubuntu 20.04.2 LTS
Kernel Version : 5.4.0-74-generic

what could be the problem ?

ha