The company said in a post on its support website that users will need to disconnect these devices before upgrading their computer to the new version of Windows 10.
"Inappropriate drive reassignment can occur on Windows 10-based computers that have an external USB device or SD memory card attached during the installation of the May 2019 update," explained Microsoft.
For example, Microsoft explained, a USB storage device that was previously mounted in the system as drive G may be reassigned a different drive letter – such as H.
Windows said that the drive name reassignment is not limited to removable drives, with internal drives also being affected.
Microsoft said it will resolve the issue in a future service update for Windows 10.