I've read several people has experienced this WP8.1 issue, and the main suggestion has always been moving everything you can to the SD. However, I've tried it all, and the internal memory is still almost full. The phone still allows me to make calls and send SMSs but I cant enter Whatsapp without getting the Storage Full message. The app can't be moved to the SD, but uninstalling it doesn't make any difference in terms of storage. With the help of Storage Sense, I noticed that the Music and Videos apps are the ones responsible for this issue. I've deleted every video and music file from the phone, but as you may know, these apps cannot be moved to the SD.
Will resetting the phone help in some way to free up space consumed by "ghost" files that might be there without me knowing?