Possible causes

PowerThe pump display connected to the X2 has either lost power or was never switched on.Make sure the power supply is operational.
CommsThe RS485 cable linking the X2 and the pump display is not connected properly at either end or is damaged.Make sure the cable is connected the right way on each end and that it isn't damaged.
AddressThe X2 might be expecting to connect to a pump display address 1, for example, but the address on the pump display is set to something else.Make sure to set the address as required.
EnvironmentalThe pump display itself became damaged from rain getting into the device or something similar and is no longer working properly.Contact Hydip to get a replacement pump display.
FirmwareAn issue either in the X2 or the pump display's firmware.Contact Hydip for assistance.