This is a well documented issue, but I must find a way to fix it in place somehow. It will take days to move the files off the server to a USB drive and merge separately. The server only has USB 2.0.
The disk where the VM is stored has no files except the .vhdx and the .avhdx files, I can't make any more space there.
I do have enough space on the server to move just the .avhdx files, but documents say they must live with the main in the same directory and disk.
There are four (4) .avhdx files, and I assume they must all remain present.