It seems like it could be an issue with the instance itself. If you haven’t done so already, verify that Nginx is running on your EC2 (or in the container) and that the port is accepting traffic.
ps aux | grep -i nginx
telnet localhost 443
Are you running Amazon Linux? I use CentOS on AWS, but you can try these commands to disable the firewall, if one is running:
systemctl stop firewalld
systemctl stop iptables
systemctl stop ip6tables
Although less likely, the traffic might somehow be blocked on the VPC, so make sure your VPC network ACLs look good.