Thumbnails not automatically generating anymore

Hi, love the plugin.

We’ve been using the plugin to cater to a members only image download section on our website.

However it seems that whenever we upload an image (jpg, png, etc) using the ‘Attach Files’ box and while the image uploads and works perfectly as intended, the images are not automatically creating the thumbnail anymore.

Have you had anyone else with similar issues and did you provide a fix? Any chance you could please help point me in the right direction? Cheers