I have been using FPD on my website for a while now and it has behaved well.
However when customers are trying to upload an image they are getting an error message advising that after trying to upload an image they are getting an error message "This File Is Not an image"
I have tested this with one of my own (Jpeg) files and am getting same error message.
I am using WP 4.9.6 & Woocommerce
Please open a support ticket so we can have a closer look at your issue and help you get it fixed.