Did you configured/used reverse proxy like Nginx ? If yes, see the nginx configuration, most likely the issue is related to Nginx and also check the web.base.url configured in the system parameters

Yes, I get this issue just after configuring NGINX, as following:

#odoo server
upstream odoo {
server 127.0.0.1:8069;
}
upstream odoochat {
server 127.0.0.1:8072;
}

server {
listen 80;
server_name mydomain.com;

proxy_read_timeout 720s;
proxy_connect_timeout 720s;
proxy_send_timeout 720s;

access_log /var/log/nginx/odoo_access.log;
error_log /var/log/nginx/odoo_error.log;

location / {
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Real-IP $remote_addr;

proxy_redirect off;
proxy_pass http://odoo;
}

location ~* /web/static/ {
proxy_cache_valid 200 90m;
proxy_buffering on;
expires 864000;
proxy_pass http://odoo;
}

gzip_types text/css text/less text/plain text/xml application/xml application/json application/javascript;
gzip on;
}

Any comment please @Niyas Raphy