By default, mapped drives are not available from an elevated command prompt or elevated PowerShell when UAC is configured to “Prompt for credentials” in Windows.
See also: KB3035277 Mapped drives are not available from an elevated prompt when UAC is configured to “Prompt for credentials” in Windows | Windows Support
This tutorial will show you how to enable or disable mapped drives availability from an elevated command prompt and elevated PowerShell in Windows 7, Windows 8, and Windows 10.