When the bolt is closed the extractor is pushed to the right and away from the rim of the case, also the extractor spring is put under full load or stretched to the maximum. Over time the extractor spring weakens and this effects extraction AND bolt jump or the bolt moving upward when the rifle is dry fired.

At the instant the trigger is pulled the extractor and the extractor spring are the only thing pushing the bolt to the rear and thus forcing the bolt locking lugs into contact with the bolt lug recesses in the receiver.

A weak extractor spring can accelerate bolt head and bolt lug wear and shorten their usable life span, the two springs that see the most usage, strain and wear are the extractor and the firing pin spring, on my shooters I replace both springs with new ones, and replace the extractor if needed, its good insurance.