I have a website named vintagecarradio that runs on Magento. It has been great to manage such a large store on this platform. However, everything was fine a while back but from a few days I have observed that the product subcategories are not getting displayed anymore in the back-end. They do not appear in the general category tree and neither they appear when I try to edit a particular product. However, they seem to be at their place and work fine when the website is browsed from the front end. Please help and advise.