On quite a few of the rearsenaled Mosins you will find that the extractor has burrs, sharp edges, and/or machining marks. This is a push feed action where the extractor snaps over the rather substantial rim at closing. Also, it does not just snap over in a straight line, it cams over. My M38 was to the point that I had to very carefully work the extractor over. Presto, no more issues. Once you for sure have the chamber clean, if the stiff bolt continues, take a round and chamber it. Extract it and examine the rim closely.
Procede at your own risk, a guy could easily work over an extractor to the point it no longer does the job right. They are available seperately and are not too hard to swap out, so it would not be th end of the world, but go slow. Good luck.