Ajax call with DB Connection 'include' gives POST 500 error - php

Question

Does anyone know why when I move a database connection 'include' out of a function and place it at the beginning of the PHP file that I get a POST 500 error? The exact same database connection 'include' works perfectly within the function. Here is the code that causes the error:
<?php
include($_SERVER['DOCUMENT_ROOT'].'/phpscripts/set_path.php'); // DB Connection Path
include 'mysqli_connect_sa.php'; // DB Connection
if(isset($_POST['row']))
{
$uid = $_POST['row'];
$response_bdls = getBDLs($uid);
$response_cg = getCompetencyGaps($uid);
echo json_encode(array($response_bdls, $response_cg));
}
Just in case you want to see the Ajax call:
$.ajax({
type: "POST",
url: '/phpscripts/ss_scbdls.php', //
data: {row : row},
success:(function(response){
response = JSON.parse(response);
loadSC_bdls(response[0]);
loadSC_cg(response[1]);
})
});
Thank you for any insights or direction you can provide.
Requested Information #1
Here is the mysqli_connect_sa.php Content:
// SA Database access information
$hn = 'localhost';
$db = 'xxxxxxxx';
$un = 'xxxxxxxx';
$pw = 'xxxxxxxx';
// Connect to DB
$dbc = new mysqli($hn, $un, $pw, $db);
// Set the Encoding
mysqli_set_charset($dbc, 'utf8mb4');
Function:
function getBDLs($candidate_id)
{
$sc_bdls = [];
$sql_query_bdls = "SELECT bdl_increment AS id, learn_load, start_date, target_date, completed_date, bdl_20, bdl_10, bdl_70, cg, cg_orn, cg_tit, cg_lj FROM bdls INNER JOIN competency_gaps USING (cg_id) WHERE bdls.candidate_id = $candidate_id";
$result_bdls = $dbc->query($sql_query_bdls);
while($bdls = mysqli_fetch_assoc($result_bdls)) {
$sc_bdls[] = $bdls;
}
mysqli_free_result($result_bdls);
return $sc_bdls;
}