Web app in AWS EC2 instance server cannot be visited

Our web apps running at AWS EC2 instance server suddently cannot be visited. The apps can be started successfully, but when visiting them in browser, we got '400 Bad request version' error all the time. We tried to reboot instance several times, we tried to create some very simple node.js or react sites, we tried to run them on different ports, but still got same problem. Our app were running well in port 5000, 5001, etc. We created security group for inbound ports already. Can anyone help?