SUMMARY: Many folders have the wrong size, underestimated 2 - 10 times OS VERSIONS: Windows 10 21H1
Same problem here. Filelight reports my file sizes wildly inaccurately, making it unusable on Windows.
That should be fixed with the latest release, where I've switched the listing code to use native API instead of compatibility code (it didn't correctly deal with symlinks, junctions and probably heaps of over edge cases)