I've got the Circuit back I'll replace it and see if it works, honestly my eyes are not trained and I don't notice the darkening that Tony refers to but I'm hopeful.

Thank you very much Spehro, I think it might just be it. I'll see if I can get the board back to fix it =)

You're right, it would need to cut the alternating signal first that would require extra hardware, a diode in series with a resistor comes into mind but there still would be a -0.7V left in the signal so it wouldn't work, maybe there are other ways but probably offsetting the signal still easier, so disregard the answer I gave @Blue and thank you Sneftel to point this out.

@Unimportant the in-circuit reading that I've got from my multimeter was showing the other way around as if it was an NPN transistor. The complementary of STF2907A as you proposed would be STF2222A which has "20F" marking instead. I don't think it could be a busted PNP because the measurement is consistently 0.735V. I measured in continuity mode with the common to the Emitter (pin 3) and the other way around it goes off the scale.

Btw the component that I'm questioning about it's not in SOT-223 package, I've put a component with SOT-223 beside and took a picture of it. I'm adding the picture on OP.

I also agree with you @Unimportant, normally I think they would also have its PCB cut underneath the optocoupler to isolate the primary from the secondary but I was able to trace pin 2 of the MR to the collector of this optocoupler.

Thank you Unimportant and KalleMP. Funny thing is that I actually found this same PCB on a Russian site but unfortunately there was no schematic and I didn't find any other sources of this same board. I'm posting the whole circuit in the OP.