Uploading multiple files – redirects to /wp-admin/admin-ajax.php

Hi there,

I am able to upload single images to a gallery no problem. But when I try and upload multiple images at once, the page redirects to /wp-admin/admin-ajax.php and the images are not loaded into the gallery.

Here is my setup, in the page editor:

[fu-upload-form class="custom-upload" title="Upload your photos" post_id="171"]
[input type="file" name="photo" id="ug_photo" class="required" description="Photo(s)" multiple="multiple"]
[input type="text" name="author" class="required" description="Author"]
[input type="text" name="post_title" id="title" class="required" description="Caption"]
[input type="submit" class="btn" value="Submit"]
[/fu-upload-form]

https://ww.wp.xz.cn/plugins/frontend-uploader/