Ok I've found something interesting
On L4981A power factor corrector IC if I place my meter probe on pin 15 suddenly bulb in series with mains dim away but relay stays activated.
PIN 15 P-UVLO Programmable under voltage lock out threshold input. A voltage divider between supply
voltage and GND can be connected in order to program the turn on threshold.
So I gues something is not right with input voltage for this IC, or does that mean faulty IC on it's own? Voltagte at Vcc
pin 19 10V
I atached datasheet for IC and bord's photos.