Time Machine Constantly Failing After A Few Seconds - 6.9.4 (Hotfix 1) - MacOS High Sierra (10.13.6)

Recently, after several months of sucessful Time Machine backups, I received a Mac system error that there was something wrong with my Time Machine backup, and the system would need to create a new one.  I clicked on OK, and the system did what it had to do.

Since then however, I have been unable to get the first (new) backup to be successful to the ReadyNas 214.  I have been able to make Time Machine backups to an external 2TB drive, without any issues.

When backing up to the RN disk , the backup goes through the Preparing backup... stage, then copies less than 1 GB of 523 GB (the most recent test got to about 300MB, and the one before, 74MB, and the one before that, about 118 MB), only to begin the Stopping...process without any other error.

On the RN itself, I have:

• removed any Private TIme Machines, rebooted, and added them again.
• removed the Public Time Machine,  rebooted, and added them again.
• rebooted the machine for the sake of rebooting.
• confirmed there is ample space for the drive, both in relation to available space on the HD and in relation to the required space for the first backup.

 

On my Mac, I have:

 

• removed any Private TIme Machines, rebooted, and added them again.
• removed the Public Time Machine,  rebooted, and added them again.
• rebooted the machine for the sake of rebooting.

 

In the HD, I have confirmed that the SparseBundle files are deleted for the drives I was removing, and created when a drive is created on the RN (image attached).

As already written, I have been able to successfully backup to an external drive without any issues.

Thanks for any insight you can provide.

6.9.4 (Hotfix 1) - MacOS High Sierra (10.13.6)