I have this issue, that maybe during update or something start vorpx disappears from my desktop. I am not sure it is related, but my dks just stopped working in extended mode also..
using oculus runtime 0.6.1 beta, windows 8.1 and nvidia 680
I happened the same case for some time, the problem for me was Windows Defender.
My solution to this problem was to update virus definition windows defender, vorpx uninstall, remove any debris in directory animation labs, and a clean reinstallation of vorpx.