.php files on NGINX - execute, but no output sent

Hi - I have an NGINX server on LAMP, Ubuntu 16.04 and have got wordpress working OK.

However, when I upload my own .php files to /htdocs, they execute, but no output is sent to the browser. I just see a blank screen. The .php files output fine on my own localhost.

I notice that the owner/group of the WP files is www-data, but from my uploaded .php from filezilla, the owner/group is root.

I have no idea what is going on here!

Thanks :)