[Q] Can't sync music to android via USB topic

I'm trying to sync about 30 gigs of music to my phone via USB. The phone is a Galaxy s4 (running AOKP, if it matters). What happens is, I connect via USB and start the syncronization process. It works great for a while (files are copied, it's all going swimmingly) and then it just stops. At this point, if I try to navigate to the external SD card via windows explorer, windows explorer freezes. Disconnecting and reconnecting fixes the problem temporarily.

There appears to be no limit to the amount of time I can have the phone connected before it fails. The failure is triggered by transferring the files. I have used mediamonkey and musicbee -- neither works.

What do?