tail -n 50 /usr/local/apnscp/storage/logs/start.log - check the backend log for any indication of what may have caused an abrupt termination (via DEBUGGING.md).
Discord’s the fastest way to tease out what’s going on. If you drop an test.html page under public/, does /test.html come up OK on the domain? If so, is a .htaccess present in there? You’ll see something similar to,
# Enable caching
UnsetEnv no-cache
DirectoryIndex disabled
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ http://localhost:40011/$1 [P,L,QSA]