Windirstat shows a large unknown something of 26gb!

I have a Samsung 128gb microsd in win10 oct update. I cannot see it in explorer. So I tried to run Ubuntu (from win store) and mounted the sd.
$ sudo mkdir /mnt/d
$ sudo mount -t drvfs D: /mnt/d
But ls -al does not list it.
Windows says I have 5.8gb free space left. Windirstat confirms that. If I add up all the dir sizes I do get 119.7gb just like Win10 says. However there seems to be something of 26 gb and I want that space back... Have no clue anymore.
I found this similar issue and tried TreeSize Free, but it does not even list the 26 gb "file"
p.s. '<Onbekend>' is Dutch for '<Unknown>'
p.p.s. the filesystem is exfat
Just tried to run docker system df and everything is 0. even when I have a MobyLinuxVM.vhdx of 2gb on my C:/
I think that I have found it. There is a huge difference between the size and allocated size for my code folder. which has archives and git repo's. that difference is shown in windirstat as some unknown thing, when treesizefree just has these two columns with size and allocated size.
