OK, this is an interesting problem.
So, I have an external SSD in a USB3 enclosure, and I've been moving my Steam Library onto it.
The SSD is a Samsung EVO 850, 500GB drive. I've tried two different enclosures, a Startech and an Orico. Both behave the same way.
The enclosure is hooked up through the keyboard base of the Surface Book via one of the USB3 ports.
The problem I'm encountering is when the drive is busy writing files the base seems to disconnect and the drive disappears. It eventually remounts, but of course the damage is done...
To test this issue, I ran Crystal Disk Mark 5 on the external drive, and the read cycle is fine. Once the write cycle begins, it seems to hang up and then suddenly the drive disconnects.
Anyone have any idea what might be going on here?