What is this large folder?

Steve C said:

Could be but there is nothing in Turn Windows Features On / Off relating to Sandbox!

What build is this?

Did you ever have this on any version of Insider, and reverted it back? Those files are Sandbox. I can see the .vhdx file, and all the Windows stuff.

That may be the only way, but one last question... did you ever have any 3rd party Sandbox software installed on there? Those folders and files had to come from somewhere.

Steve C said:

No third party sandbox programs. The only thing I did recently was to install Windows Defender Application Guard for Edge then remove it.

This is an excerpt from an MS Doc on Application Guard. https://docs.microsoft.com/en-us/win...s-wd-app-guard



That may well be what you have.... leftovers from it after removing. I would think removing it would take it's files with it, but maybe not. Or it was not completely or totally correctly removed.

Reading this article, it is just a add or remove feature in Windows. My bet is it did not clean up the folder, just uninstalled the code.

How to enable Microsoft Edge Application Guard on Windows 10 April 2018 Update | Windows Central

If possible, for safekeeping, copy that whole Containers folder somewhere, and delete it. You may need to take ownership of the folder and contents.