sockstat -4 | grep 80 is really empty? Usually its only the redirect rule
root@OPNsense:~ # sockstat -4 | grep 80root ntpd 3210 31 udp4 192.168.180.1:123 *:*root lighttpd 58302 4 tcp4 127.0.0.1:43580 *:*root nc 31856 3 tcp4 127.0.0.1:8080 *:*
Another reason could be that you define stream servers and http servers in nginx using port 80. Then nginx blocks itself.
Now we will never know ... But it seems it was just a small problem somewhere ..