The authenticated check is done here:

https://github.com/SSilence/selfoss/blob/9a1b107fd3d05dfa7f4cfb74d52293d0fef4aff7/helpers/Authentication.php#L66

Could you try dumping some more info?

--- a/controllers/Index.php
+++ b/controllers/Index.php
@@ -17,6 +17,13 @@ class Index extends BaseController {
      * @return void
      */
     public function home() {
+        var_dump(\F3::get('public'));
+        var_dump(\F3::get('auth')->enabled());
+        var_dump(\F3::get('username'));
+        var_dump(\F3::get('password'));
+        var_dump(file_exists(__DIR__ . '/../config.ini'));
+        exit;
+
         // parse params
         $options = [];
         if (\F3::get('homepage') != '') {