move_uploaded_file - File only changed after directly loading that page - php

Question

So, I'm making a chat room and I want to allow my users to upload a profile image. I know the AJAX is working, and the file is being uploaded and moved to users/[their username], but on other accounts their profile image isn't changing to the new one until they load up the actual profile image.
It's kind of confusing, so I'll simplify it:
User successfully changes profile image (file is uploaded)
Same user goes back to the chat room and the their profile image has changed
New user who was on the chat room before the new profile image was uploaded reloads the page to find the profile image of the other user is still the same.
Also, I've found if the second user goes to the file that contains the other user's profile image, it hasn't changed, but on reloading the image file it does. It's very confusing and I have no clue why all this is happening. There aren't any errors either. Here's my code:
(I've also tried copy instead of move_uploaded_file)
if(!isset($_FILES["profileImage"])){
echo '<script>window.setTimeout(function(){window.location = "messageRoom.php";}, 3000);</script>';
die("No image recieved.<br>Automatically redirecting in 3 seconds...");
}
$target_file = "users/" . $username;
$file = $_FILES["profileImage"];
if(!exif_imagetype($file["tmp_name"])){
echo '<script>window.setTimeout(function(){window.location = "messageRoom.php";}, 3000);</script>';
die("File type not an image.<br>Automatically redirecting in 3 seconds...");
}
if(filesize($file["tmp_name"]) > 2000000){
echo '<script>window.setTimeout(function(){window.location = "messageRoom.php";}, 3000);</script>';
die("Image size over 2MB (".(round(filesize($file["tmp_name"])/100000)/10)." MB)<br>Automatically redirecting in 3 seconds...");
}
/*Deletes file if it exists*/
if(file_exists($target_file)){
unlink($target_file);
}
if(move_uploaded_file($file["tmp_name"], $target_file)){
echo "The file '" . basename($file["name"]) . "' has been uploaded to " . $target_file . "<br>Automatically redirecting in 3 seconds...";
} else {
die("Error in file upload.<br>Automatically redirecting in 3 seconds...");
}
Also, in the code it looks like $username and $password aren't defined, but they are defined earlier. Please help, I have no clue what's going on.
Finally, this needs to be able to override pre-existing files, I want the user to be able to change their profile image.
Thank you so much!!!