Time Machine Waiting to Complete First Backup
New Seagate 5Tb external drive. It took me a few tries to initialize/format, and it now seems to be working fine except for Time Machine. I get an error message from the operating system that warns me to “eject the drive before disconnecting.” I am not touching the drive while it is backing up. Time Machine gets stuck on the task “Waiting to Complete First Backup.” I have manually started the backup a couple of times and each time progress seems to be made, but the backup never finishes because of the error message. I have left the backup run unattended overnight. All attempts end the same way.
I searched the archives to see what I might be able to do now. I wasn't able to find anything that made sense to me. If I'm missing something, please point me in the right direction.
Thank you.
macOS Sierra 10.12.6
MacBook Air (13-inch, Early 2014), iOS 10