Also, according to the Microsoft information about this folder it should, by default, be placed on my %SYSTEMDRIVE% but for some reason it appears on my DATA drive....
Modify Cache Drive
This setting allows for an alternate Delivery Optimization cache location on the clients. By default, the cache is stored on the operating system drive through the %SYSTEMDRIVE% environment variable. You can set the value to an environment variable (e.g., %SYSTEMDRIVE%), a drive letter (e.g., D:), or a folder path (e.g., D:\DOCache).
The update process in Windows 10 and Server 2016 is nowhere near as reliable, speedy and efficient as that on previous Windows OSs so I assume I'll just have to add this issue to the long list of others.