Thanks for the suggestions.

I do use BiaB on a desktop.
The back USB ports are used for other devices.
I don't use a hub on this computer.
All devices are directly connected.
Yes, I always connect both ends of the Y-cable.
A loose cable? I doubt it. But I'll check next time it happens to make sure I haven't pushed against anything.
I notice that 2013 came with a new model hard drive than before.
Maybe an issue with it?
No one else having this problem, huh?