A gunsmith familiar with the SKS is the best path.
Looking at the picture of that pin it looks like at least a few times during the gun's history, the hammer followed and jammed the pin. I would black marker it and the hammer face to see if it is happening again. (Red arrows in pic)
When it misfires, you can pull the trigger and hear the hammer fall?
The shoulder/ bolt contact surface can be blackened to see where the edge hits. (Blue arrows)
Tight headspace can cause action issues. I doubt it's excessive headspace.
You can check headspace with shim stock. Use your normal malfunctioning ammo. It would be best to use dummy rounds but at least pull the pin and ease the bolt into battery. Then remove the cover and recoil spring. Push forward on the carrier and check with shim stock. Even with the pin pulled, a live round in the chamber you need to observe loaded gun protocol. There is nothing to hold the bolt/carrier if the round fires.
The rear surface of the carrier (Green arrows) seems to be contacting the rear of the receiver.
That could be a sign of a weak recoil spring.
The gas system may be a problem but if the action picks up a round, goes into battery it should fire.