The water inlet valve on the back of the unit where the water supply comes in can have a slow leak and will cause ice to buildup and block the fill tube. Disconnect the ice maker line from the valve and watch to see if it has a slow drip. It doesn’t take much to eventually block the fill tube.
The valve can leak because of sediment in the water preventing it from closing or low water pressure.

Try swapping the wires on the dual water inlet valve. Then try the water dispenser. The water should go to the ice maker. This will tell you weather or not the ice maker valve is working and if the line is clear.