Thanks for the information.
I did find the firmware for NVR4216-4KS2. My unit is not a S2. I don't believe they are the same firmware. NVR4216-4K vs NVR4216-4KS2
I was hoping there would be an updated firmware available for NVR4216-4K as well. It also has the frame dropping problem. Does anyone know if it is available? @empirecandy