If you try to access your slim routing with some query string parameter, like http://foo/bar?parm=balabala, you will probably get a 404 response.

The main reason is, the documented config of slim is telling you to rewrite the uri by:

try_files $uri /app/github/index.php;

try to update it to:

try_files $uri /app/github/index.php?$args;

see a post of discussion deeply hided in the froum.