Attention: Before you commence any electrical work, please be sure to turn off the power supply or consult a qualified electrician to seek further advise.
First you need to check if the wiring was done correctly: be sure that every wire is in the right position (as shown in the picture).
If the problem doesn’t go away check the origin of every wire: sometimes the wires colour doesn’t reflect the standard wiring so even if it seems that the wiring is correct it may be that the wire itself leads to the wrong connection. Verify if this is the case and rewire correctly.
L / R = Live input
N = Neutral input
L1 = Switched Live output to Lamp 1
L2 = Switched Live output to Lamp 2