Thank you so much GTAUS for your time. I am at the point where I have to either:
1. REFORMAT STORAGE SPACE WITH A 16K CLUSTER SIZE for MS Storage Spaces, which means reformatting the drive in powershell and then rewritting everything back, all 17tb from my Synology NAS backup. A few days work.
2. Switch to Drive Bender, learning curve (find the app interface ugly)
3. Switch to DrivePool, learning curve (much more pleasant interface)
But I have heard that Drive Pool is a better programmed piece of software. The problem is that comment is from 2016! It was due to DrivePool's low level drivers.