Windows says a folder is >5GB in size, but it doesn't appear to be when checking manually?

[Happy Crayfish]

Having a weird issue with a folder in my D:\ drive.
When I right click the folder and go to properties, the folder is, according to windows, over 5GB in size:

But when I open the folder and press CTRL+A and open the same properties page, it tells me all of the files are only 600MB in total size:

Does anyone have any idea why it does this?

Edit: Just noticed it also says there are over 5000 files in the folder, but only a few hundred when doing it manually.
Edit 2: For some reason Gyazo took a fullscreen picture instead of only the explorer windows >.>

 

[therealduckofdeath]

If you click on the tab "visa" and check the box "visa dolda filer" you might see more files and folders.

 

[rgd1101]

use windirstat https://windirstat.net/

 

[Happy Crayfish]

If you click on the tab "visa" and check the box "visa dolda filer" you might see more files and folders.

There were 2 hidden, very large files:

Thanks a lot for the help! =)