The arduino is driving 3 relays which switch on/off a pump (220 VAC) and a power supply (220 VAC) . Could there be an interference problem, though this is unlikely since the remainder of the circuit (except the LCD) is working perfectly.
This is most likely the cause of your problem. There have been lots of fairly recent posts dealing with similar erratic operation when relays and/or motors are involved.
Some things to look into:
How are you powering your relays?
Do the relays have diodes across their coils?
How long are the wires leading from the Arduino to the LCD and how are they routed?
Are there extra bypass/decoupling capacitors on your power leads?
Don