I was well on my way to plotting the 91st plot on my 10TB drive. Then, it froze. The log indicated there was not enough space to complete the transfer from the SSD. I forget the exact numbers, but it seemed at the time there was plenty. This is a new drive with nothing else on it but chia plots.
Emptying the recycle bin does not always empty it, in that it may appear empty but actually takes up space.
I have two 16TB drives, one drive had a different amount of free space and one less plot than the other. When I used Treesize Free by Jam Software, it showed the recycle bin size at around 20GB, a simple right click and delete freed up the space.
Update: I was able to easily transfer a completed plot on another drive onto this one. Now shows 91 plots, with only 89.7GB free. I have no idea why I was originally unable to complete this last plot, but no matter. Problem solved.