I had the same issue with our 722 last year. After sending it back to Sound Devices, this is what they found:
"The technician working on this unit has determined the fault lies in a A Ball Grid Array FPGA. Sound Devices does not have the facilities to reliably replace this component. I have confirmed the fault.
Cooling this component allowed the unit to ...
Not recommended to go too far - C.Link definitely won't do ya. And as far as I know, there isn't a signal strength booster/interference guard.
BNC should work for 50 foot runs though.
I had referenced an audio-tech sales employee about this for doing gun-range recording. Also, here is an online reference: