My system nudged me to let it install the Windows 10 Fall Creators Update. Like any sane individual, I decided to run my backups first. This normally takes around forty minutes.
Four hours later and without a single file yet transferred, I discovered that Windows helpfully downloaded the update into a directory called $WINDOWS.~BT – and the backup program was stalling for ten seconds on each and every tiny file in it because...?
No idea. *sighs*