While loop doesn't wait before displaying - php

Question

In this code section, the query gets all the teachers and appends their assigned classes within the object
The weird thing is it works perfectly on local but not online, it is almost it doesn't wait for the while loop
<?php
$SID = mysqli_real_escape_string($con, htmlspecialchars($_POST["SID"], ENT_QUOTES));
$allTeachersArr = [];
$test = [];
$q = "SELECT onderwysers.*,klasse.Klas,klasse.Datum,klasse.Vak FROM `onderwysers` LEFT JOIN klasse ON onderwysers.ID = klasse.Teacher WHERE `SID` = '$SID'";
// echo $q;
$result = $con->query($q);
if ($result->num_rows > 0) {
while ($row = $result->fetch_assoc()) {
$subjectItem = new stdClass();
$filtered_array = [];
$isIn = false;
$var1 = $row['ID'];
$var2 = $row['Teacher'];
if (count($allTeachersArr) > 0)
foreach ($allTeachersArr as $item) {
if ($item->ID == $var1 && $item->Teacher == $var2) {
// do something
$filtered_array = $item;
$isIn = true;
}
}
if ($isIn == true) {
$notAdd = false;
// echo "updates";
$subjectItem->Klas = $row["Klas"];
$subjectItem->Datum = $row["Datum"];
$subjectItem->Vak = $row["Vak"];
foreach ($filtered_array->displaySubjects as $item) {
if ($item->Klas == $row["Klas"] && $item->Vak == $row["Vak"] && $item->Datum == $row["Datum"]) {
// do something
$filtered_array = $item;
$notAdd = true;
}
}
if ($notAdd == false) {
$temp = $filtered_array->displaySubjects;
array_push($temp, $subjectItem);
$filtered_array->displaySubjects = $temp;
}
} else {
//add new entry
$subjectItem->ID = $row["ID"];
$subjectItem->Title = $row["Title"];
$subjectItem->Name = $row["Name"];
$subjectItem->Surname = $row["Surname"];
$subjectItem->Afkorting = $row["Afkorting"];
$subjectItem->IdentityNumber = $row["IdentityNumber"];
$subjectItem->Geslag = $row["Geslag"];
$subjectItem->ContactDetails = $row["ContactDetails"];
$subjectItem->Email = $row["Email"];
$subjectItem->RegKlas = $row["RegKlas"];
$subjectItem->Status = $row["Status"];
$subjectItem->UID = $row["UID"];
$subjectItem->displaySubjects = [];
array_push($allTeachersArr, $subjectItem);
}
}
}
echo json_encode($allTeachersArr);
$con->close();
THE EXPECTED RETURNED DATA(This is local, online returns nothing)