Questions on snubber circuit
The wanted source for triggering isn't clear. I guess the ignition spikes are wanted to cause triggering.

In the guessed case the capacitance between wires, maybe only 30pF, makes a capacitive voltage divider with C1. It drops the voltage to about 1,5V which should be enough for triggering.

Resistor discharges the remnants of the previous pulse. D1 kills the wrong polarity signal which surely occur because the ignition pulse very likely oscillates a moment. That's not a miracle because the coil and the wires have capacitance and inductance - there's a resonant circuit as a side product.

ADD due the comment: 220nF can be too much if your connection capacitance is substantially less than 30pF. To get 30pF the TRIG wire should be wounded around the HV wire several turns. You can calculate the available capacitance if you know the dimensions and materials.

The result with 220pF is unpredictable. You will get higher peak voltage, but the current pulse into the gate will be shorter. That can prevent reliable triggering. But also false triggerings can happen more often. I do not believe it kills the thyristor because the energy injected into the gate per an ignition is only about one microjoule. You need quite high speed motor to get a substantial power. Even 1mW needs 1000 ignitions per second.

Make a test with real ignition. Use the largest C1 which keeps the triggering reliable. Drop C1 about with 25%...50% steps 220nF, 150nF, 100nF...

100kOhm can be too much to suck all remnants fast enough. RC time constant must be much shorter than the pulse repeating period. 220pF and 100kOhm can be ok together.