I also came across another problem, and I think some one else had this previously and I could not work out the cause of the issue. I’ve not used my plot mover since last October so consequently I forgot how to use it! I started trying to add the mounted folders to it, of course once I tried to add the second folder it complained the drive was already in use. So I added drive letters to the other drives.
This left one destination as C:\Plot - Mounts\drive 1 so when the program gets the free space on the drive Windows returns the free space on C drive!! So it meant when the transfer kicked off I got an out of space warning.