Try flushing with lighter fluid. The only things I can think of are the sear may have become rougher from use or grit. A stoning and polish may fix this.

The sear on the bolt can seat differently in the action and create a different feel or pull weight. It could be a timing issue and the tension from the extractor could be enough to cause the trigger and bolt sears to engage differently. Hopefully a pro like Redneck who really knows will respond.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli