Are you on the latest firmware?
I have had 2-3 NVX units on campus running the latest firmware that appearently just stopped working, they are online with the processor etc.
Kind of "lights are on but nobody home".
One of them was factory reset and came back to life, the others needed a reboot.
A vague feeling of fw issue, but haven't been able to prove it or dig any deeper.
?
Brgds
Jon Torstein