How to View Time Machine Data via Disk Expert

Since first installing El Capitan I keep “losing” huge amounts of disk space off my primary Mac drive.
I should point out that Disk Expert is the ONLY utility that at least recognises this space by simply referring to it as “Inaccessible Disk Space” (see below). I have tried reinstalling El Capitan from scratch and then using Migration Assistant to restore all my apps and data. This seemed to do the trick however about a week later the “Inaccessible Disk” space suddenly returned.
I have googled this issue and ruled out all the usual suspects such as local Time Machine files, hidden directories etc etc but so far have had no success.
I am now totally desperate and was wondering if you could suggest anything I should try to fix this problem.
inaccessible-disk-space-disk-expert

Typically it happens if your disk has some data that were created with root/admin access.
Disk Expert can see that some extra files or folders exist, but can’t touch the files to get any information (as any other application on Mac).

It often happens with Time Machine saved data, nevertheless the app can’t get any info and even can’t mark the data as Time Machine backup or something else. To view these files you just need to launch Disk Expert with the same user rights as files have.