Perform a reset of the network settings when the PoS has issues communicating to the GK420D. Usually, the PoS will send a message that the printer is disconnected, and re-pairing the printer does not solve the issue.
Hold the Feed button down through 1 blink of the green light, 2 blinks of the green light, 3 blinks of the green light, and 4 blinks of the green light.
After the round of 4 blinks of the green light, stop holding the button. The light should turn red. Hold the button down until you get 1 blink of the green light.
If done correctly, this should reset the printer. The light should be red and blinking during this reset period. Once it is finished with the network reset, the light should become solid green. At this time, a printout of the settings can be obtained by holding down the Feed button for 1 blink of the green light.