The problem of my Sansa MP3 player disconnecting whenever I would trying to transfer data was driving me **nuts**. It would happen when I copied files directly or when I tried to add Audible audios. I read in forums that the Sansa can not keep up with rapid data transfer and so you need to switch to a USB 2 port, but that did not help me.
But I FINALLY found a solution: a USB 1 port !!!
I have a little USB combo hub card reader very similar to this one: https://www.amazon.com/ERCRYSTO-USB3-0-Reader-External-Memory/dp/B072R4M3VQ/ref=sr_1_9?keywords=USB+combo+hub+and+card+reader&qid=1567304924&s=gateway&sr=8-9
In addition to reading SD chips, It has 3 USB ports, USB 1, USB2 and USB 3. If I plug the Sansa in to the USB1 port, data transfer works like a charm.
By the way, I do not represent the company selling the device I linked to. I have no skin in this game other than wanting to help others avoid the pain I endured. If you can find another way to add a USB 1 port to your machine, I suspect it will work just as well.