Symptom summary
Windows Defender Application Guard (WDAG) or Windows Sandbox might fail to open with the error, "ERROR_VSMB_SAVED_STATE_FILE_NOT_FOUND (0xC0370400)" or "E_PATHNOTFOUND (0x80070003)".
Workaround
To mitigate this issue after receiving one of the above error messages, you will need to restart your device.
Next Steps
Microsoft is working on a resolution and will provide an update in an upcoming release.