Lenovo TB3 10 inch tablet

I have 16 Gb of internal memory available with 4.52 Gb used and when I try to add a simple app told to delete files to be able to do so. I moved every app that I could to my SD card and it freed up some space. I tried All-in-one Toolbox, Disk Usage and Total Commander and none can find the 10 Gb missing in internal storage. Thought it was some sort of delete issue as the table does not have a delete app icon or a delete file that I could find looking at both open and hidden files. Any ideas of what to try next?