Storage Almost Full message

I have an iPad Air 2 64GB, an iPhone 6 64GB and an older iPad Retina 3rd Generation 32GB all running iOs 8.2 or whatever the latest. I use the same Apple ID to login on all of them for messaging, email, iTunes, App Store, etc. I receive the "Storage Almost Full" message at least once a day on them all. If I look at my usage on any of the devices, it will show under 1GB of storage Unused on them all but less than 10GB of Photos and Apps. If I power of fthe device, hold the Home button while I power on and let the Apple logo appear, go away and reappear and then release the Home and power buttons, it will show true usage afterwards. For example, I just received the message on my iPad Air 2; it was using 54GB and had 1GB Unused. I powered off and on and now I am using 12GB and have 42GB Unused. I have called and talked with Apple Suport and they had me delete some photos and sync with my computer, change a couple of settings and they called it good to go. Yet, I still receive this message. It is like there is a memory leak, the iOS has a bug or an app goes wild. Anyone else have this happen and know how to fix it?