Hi,
I can't find a snubber.
I have a problem with BT136, not MOC.
Let's say you have a LED, rated with 20mA...and a current limiting resistor, wrongly dimensionated to supply the LED with 50mA.
The LED fails.
For sure you can say you have a problem with the LED then, but the resistor is responsible for that..
***
A device mainly fails because of overvoltage, overcurrent, overtemperature...(all short time or long time) thus I questioned these three items.
I see no protection against overvoltage, (caused by stray inductance)
I see no protection against overcurrent (load inrush current, gate current)
I see a driving circuit not according datasheet
It seems you don't want to modify a thing, so what "helping answer" do you expect?
It surely won't help if one says "you made everything right".
Klaus