Hello,

I would recommend first checking your Nginx error log for some more information:

sudo tail -100 /var/log/nginx/error.log

It is possible that there is an issue with the Nginx server block, feel free to share it here so I could advise you further.

I could also suggest taking a look at the steps here on how o troubleshoot common Nginx problems:

https://www.digitalocean.com/community/questions/how-to-troubleshoot-common-nginx-issues-on-linux-server

Regards,
Bobby