I had this problem, but a very recent article on OSXdaily.com had a fix for the USB port that solved it. Apparently after an OSX update, sometimes the USB port become flakey. Doing an SMC reset somehow fixes the USB port to normal. I have pretty sure that it was a software problem, rather than a failed Ixpand drive. In my experience with Sandisk products, I have not seen one hardware failure.
Reference: Mac USB Ports Stopped Working? It’s Likely Easy to Fix; http://osxdaily.com/2015/08/09/mac-usb-ports-not-working-fix/
