Helpers not working after moving from Xampp to Linux server

I've moved my first CI4 project from Xampp to my Linux server tonight.  I followed the directory structure from the configuration documentation (where everything except the contents of the "/public" folder sits outside of public_html and the "/public" contents go in the public_html folder).  I kept the entire directory structure intact from the Xampp configuration.  I changed the baseurl.  Everything works except for pages that call custom Helper functions; it's saying those functions are undefined (but they work fine in the Xampp build).  Would anyone have any idea why the system wouldn't be finding / seeing the Helper functions in the new environment, even though the directory structure is identical and all other functionality works?