Just checking, you did issue the 'usbsd' command to JeVois over serial port, right? The virtual USB flash drive does not automatically show up when JeVois starts up. You need to request it.
We have some instructions here:
http://jevois.org/doc/MicroSD.html
last section at the bottom of the page.
It works ok here with Linux, OSX, and Windows 7 but I do not have a Windows 10 machine. I will install one at some point if the problem persists.
The brief appear/disappear that you see may be related to the fact that we do announce the drive to the host from the beginning, but we announce it as an unloaded removable disk drive (like a CD-ROM drive with no disk inside), so Windows 10 may hide it until it appears to be loaded. The 'usbsd' command does that.