Had the same thing happen last year with my Sako .243. Took the bolt apart and solvent cleaned it. The professional advice I received, was to be very sparing with any lube in the bolt. Some said no lube, some said use G96 lightly, add others said use Molly Lube on firing pin.
After cleaning the bolt, I put a very light coat of G96 on the firing pin and reassembled. All has worked well since. G96 is supposed to have very good cold weather properties.