Time Machine - Backup drive disappears
Hello, Problem is: LaCie Backup Drive disappears - a couple hours after waking from Sleep mode, icon for LaCie Drive is gone, with message "LaCie Disc not Ejected Properly", consistently, and not showing in Finder. Reboot iMac, drive shows up fine. New LaCie drive (from Apple Store, installed April 30). I am fairly certain but not 100% sure that this problem started after latest OS X update (10.15.5) on May 26. Have checked cables, tried different USB port on computer, Ran Disk Utility on both iMac and Lacie (strange, first try always says "Error, disk could not be unmounted", then second try no issues). Reset PRAM and SMC, contacted LaCie by email, talked with Apple Tech Support, all in that order. Something else I have noticed: when opening Time Machine, hash marks on right side indicating various iterations of backups are red, don't remember ever seeing that. Any assistance appreciated Thank You, iMac (Retina 5K, 27-inch, Late 2014), LaCie 6TB D2 Professional Desktop Hard Drive.
iMac with Retina 5K display, macOS 10.15