Laravel session::has('key') doesn't exist after new request - php

Question

First time working with Laravel and a bit confused.
Performing ajax request into controller action and after next request session key I've stored before doesn't exist.
The purpose of this code is to save some set of images and store their names to session for further work..
Session ID's equal in my parent page and ajax request. Application has no user authenticaton yet.
(Upd) Session driver is 'file' by default.
Why session key doesn't save normally?
public function upload(Request $request)
{
$rules = ['photo.*' => 'image|mimes:jpeg,png,jpg|max:2048'];
$validator = Validator::make($request->all(), $rules);
$files = [];
$fileNames = [];
$errors = [];
if ($validator->fails()) {
$errors = ArrayHelper::getFinalValuesRecursive($validator->errors()->messages());
} else {
foreach ($request->file('photo') as $key => $value) {
$imageName = $key . md5(time() . $key) . '.' . $value->getClientOriginalExtension();
$value->move(public_path('uploads'), $imageName);
$fileNames[] = $imageName;
$files[] = '/uploads/' . $imageName;
}
$sessionFiles = [];
if (Session::has('photo')) {
$sessionPhoto = Session::get('photo');
foreach ($sessionPhoto as $value) {
$sessionFiles[] = $value;
}
}
Session::put('photo', array_merge($sessionFiles, $fileNames));
}
Javascript
$(document).ready(function () {
$('#photo').on('change', function () {
var fileData = $('#photo').prop('files');
var formData = new FormData();
for (var i = 0; i < fileData.length; i++) {
formData.append('photo[]', fileData[i]);
}
formData.append("_token", $('input[name="_token"]').attr('value')); //csrf
$.ajax({
url: '{{route('adverts.upload')}}',
dataType: 'text',
cache: false,
contentType: false,
processData: false,
data: formData,
type: 'post',
success: function (response) {
response = $.parseJSON(response);
if (response.errors.length) {
for (var i = 0; i < response.errors.length; i++) {
$('#image_errors')
.append('<div class="invalid-feedback" style="display: block;">' + response.errors[i] + '</div>');
}
} else {
$('#image_errors').html('');
var totalFile = response.files.length;
for (var i = 0; i < totalFile; i++) {
$('#image_preview').append("<img src='" + response.files[i] + "'>");
}
}
}
});
});
});