What happens if you short the coil (i.e. remove L1/C1) leaving R3 connected to R4 and pin2? That should work as normal (if the resistor values are correct) as pin 2 should be about 4V which should be just greater than the trigger value. Shorting R4 with a jumper should then trigger the circuit as now. If it is inconsistent without the coil in there then the R3 value is likely too low and needs to be 680K instead of 560K (to raise the voltage at pin 2 above the trigger voltage). The latch up is strange though, I’d expect it to always trigger or never trigger not latch up. It may be worthwhile to put a capacitor between ground and VCC to make sure current spikes aren’t causing VCC to drop, but I don’t think we are drawing enough current to make that likely.
Peter