Thanks ron4mac!
This was tricky because I had to disable my custom header and footer just to get logged in as the Admin to change the debug settings, because those two pieced of code get executed even when loggin in as Admin. But your suggestion worked. :-)
Then I re-enabled the header/footer code and hit refresh to learn that the $_SERVER['DOCUMENT_ROOT'] reference failed, producing "" (Null string) instead of the name of the document root directory. Therefore all my pathnames for subsequent file_get_contents calls were bogotoid. I guess part of the blame is mine for not having adequate error handling.
EG:
$ROOT = $_SERVER['DOCUMENT_ROOT'];
// The lists below are 2 dimensional non-associative arrays:
// [ [ "0", "1" ], [ "0", "1" ], ... [ "0", "1" ] ]
// Column 0 is the value, column 1 is a description.
// FORBIDDEN_ASNS
$JSON_ARRAY = json_decode (file_get_contents($ROOT."/xxx/yyyy/FORBIDDEN_ASNS.json"),TRUE);
$FORBIDDEN_ASNS = array_column ($JSON_ARRAY, "0" );
$FORBIDDEN_ISPS = array_column ($JSON_ARRAY, "1" );
// ALLOWED_ASNS
$JSON_ARRAY = json_decode(file_get_contents($ROOT."/xxx/yyyy/ALLOWED_ASNS.json"),TRUE);
$ALLOWED_ASNS = array_column ($JSON_ARRAY, "0");
$ALLOWED_ISPS = array_column ($JSON_ARRAY, "1");
// VALID_COUNTRIES
$JSON_ARRAY = json_decode(file_get_contents($ROOT."/xxx/yyyy/VALID_COUNTRIES.json"),TRUE);
$VALID_COUNTRIES = array_column ($JSON_ARRAY, "0");
So as I suspected the "Inspekt" superCage was still in effect within the function that was called from within the Custom Header php.
Now, if I update the code to use Inspekt semantics to extract the name of the root directory, everything else on the website will break, so I am going to have to maintain two separate versions of the above code from now on... one for use inside CPG, using superCage to get the DOCUMENT_ROOT, and one for use everywhere else. I'm not going to adopt Inspekt at my root level because I personally think it's useless. I might just become willing to say to hell with it and just hard code the name of the Document Root. As Johnny Carson would say, "Weird crazy wonderful stuff, let's welcome a great wacky comedian who can always stir things up, 'superCage' !!!"