My Cloud Mirror (Gen 2) USB Drives Won't Sleep

I have an 8TB My Cloud Mirror. I attached a Seagate Expansion Desk 3TB USB drive. When the My Cloud Mirror goes to sleep, the USB drive does not sleep. If I connect the USB drive directly to my computer, it sleeps just fine. But, not when attached to the My Cloud Mirror. Any suggestions on how to remedy this situation?

SOLVED. Attached USB Drive back on Windows 10 desktop, formatted the drive NTFS, reran the Seagate software and reset the inactivity timer. Reattached USB drive to MCM, and it now works fine.

Thank you for the update and the solution !