Hi Ben,
I just tried a KMotion + 2 SnapAmps with V4.19 and it works ok.
Not sure what the problem may be. Were the lights blinking before you updated the firmware?
The "I'm alive" LEDS should always blink even after running the C program to set the peak current limits. But after setting the peak current limits the fault light should go out.
You might try connecting one SnapAmp at a time (remove any jumper to address it as SnapAmp#0). Disconnect everything except +5V to KMotion and the connection between KMotion to SnapAmp.
Check the 16 pin ribbon cable for any shorts.
Otherwise you can send it to us for diagnosis.
Good Luck
TK