Shiny server gives "Page not found" selectively to a specific parent directory

The directory privileges are identical to the one where the app.R works:

rstudio@ip-172-31-30-19:~/nlp$ ls -ld shiny
drwxr-xr-x 2 rstudio rstudio 4096 Dec  9 13:38 shiny

And in both places the owner of the directory is the user: rstudio