Hi,
I found this problem with large file sizes too.
There are several weird files, which appear to be very large in SpaceMonger, but in fact, they are small.
Later I have discovered, that recently, Microsoft introduced at least 2 new Reparse Point types, which are similar to Symlinks, but not quite.
I have found some information on google, you might want to have a look at it:
https://lifeinhex.com/running-windbgx-on-windows-7/
https://forum.exetools.com/showthread.php?t=18391
https://bvckup2.com/support/forum/topic/854
http://www.zezula.net/en/fstools/filetest.html
Here are some typical examples.
C:\Users\username\AppData\Local\Packages\SpotifyAB.SpotifyMusic_zpdnekdrzrea0\LocalCache\Local\Microsoft\Windows\Caches\cversions.1.db
is a reparse-point with tag 0x80000018 IO_Reparse_Tag_WCI
Displayed size: 8589934592 B, size in explorer: 16384 B
C:\Users\username\AppData\Local\Microsoft\WindowsApps\MicrosoftEdge.exe
is a reparse-point with tag 0x8000001B IO_Reparse_Tag_AppExecLink
Displayed size: 8589934592 B, size in explorer: 0 B