It depends on who you ask... there are lots of theories but no official disclosures.
I have two early models, and have never had an issue with either, but I do know that when they were in production some folks had feed problems and Ruger re-engineered the bolt to add a cartridge guide on the in-side opposite the extractor. (These are often referred to as having two extractors but that is a bit of a mis-nomer.)
I heard a few tales of the late (2 "extractors") model suffering a broken bolt (at the breach face) when the inside "extractor" came loose and jammed up the works... I've never seen pics of such, but apparently the complaints vs overall sales numbers convinced someone at Ruger the 10/22M should perish... and so it did.