To understand problems with a firarm you must understand how it is supposed to work. They key lies in the 8 step cycle of operation.
When a problem arises look first at the step BEFORE the problem. Failure to fire is frequently a locking problem. Failure to extract is commonly an unlocking problem.
Since yours is exhibiting both I would look at the lock up. Check that the barrel extension is timed correctly. Look at the bolt locking lugs for uneven wear that might lead you to believe the extension is off a couple of degrees.