I was having the same lag problem, it turned out to be poor shielding on the nvidia shield and lack of shielding on my usb ssd cable. You need to get a higher quality shielded usb ssd cable; the rf shielding on the nvidia shield is non-existent, a poor design. Reposition the ssd away from the nvidia shield. If you are still having lag problems after that wrapping the usb/ssd cable in aluminum foil seemed to clear for me...

Mine will lag a little bit every once in a while, but I haven’t had anything like that happen so far.

My console was too close to my TV and was interfering with it, I moved the Shield TV box to a new location and everything works awesome now.....try it.....it's something easy to try, worked great for me!

It sounds stupid, but swap the cr2032 cells for fresh ones. It fixed it right up for me.