The pins for the filament sensor belong to the 6-pin header pins near the centre of the lcd module. The top two pins, in the right column of pins are used. There is a problem with the choice of connector JGAurora have used.
Note: This issue has been resolved by JGAurora in recently manufactured machines by using hot glue to both insulate the other pins, and to hold the connector in place correctly.
When you try to print, the print may stop (or may fail to start at all), and instead the printer will make a loud beeping sound.
The printer is thinking that the filament has run out, and it is waiting for you to reload the filament before proceeding.
However, this function can be triggered by mistake when there is still filament remaining. This typically may occur via one of two ways:
Checking the sensor is plugged into the right pins is easy: the connector plugs into the block of six pins near the centre on the back of the LCD screen. The correct pins are the top two pins, in the right column of pins, in that block of six pins.
The other way this problem can be triggered, is if the connector is touching the other pins.
The connector that JGAurora has used are called JST-XH connectors. These connector have both pin sockets and side contacts. If these side contacts touch the neighbouring pins, this can also trigger the problem.
Edit: DaHai has since done a very clear video you can watch here showing the whole issue, and the solution described below!
A simple solution is just to unplug the two wire cable sticking out of the LCD module! You can access this cable from the hole underneath the printer LCD screen, or by opening up the main chassis. However, if you want to use this feature, you can do this simple trick. Turning the connect 180 degrees, will make the metal side contacts face away from the other column of pins. Note that the JST connector they are using has three sockets, but only two are used. You need to make sure that the two wires are still connecting to the same two pins, but in this case we are effectively reversing the polarity. This is not a problem – the sensor is a simple mechanical switch, so it does not matter which way electricity flows.
If you wish to use this filament run-out feature reliably, you will either need to replace the connector with a 2-pin header cable, or turn the connector around 180degrees so that the metal contacts on the side are facing away from the other pins.
The way the plug comes installed from the factory is shown in the image below. It is still recommended to flip the connector 180 degrees to orient the metal contacts away from the other neighbouring pins.
(Top Image Credit: Markus IngK - MCK, Bottom Image Credit: Riccardo De Giovanni via Facebook)