Stock? If it was pillar bedded check the pillar length. Just dealt with this issue. There is a possibility that the back of the shell isn't coming in enough contact with the face of the bolt.
On my particular rifle, the bolt would grab once in awhile, then slide over the round. Upon closer inspection, and comparing to another rifle, the bolt , when open with a round in the magazine, should be approx. 1/16 of an inch lower than the top of the round. Check that and start there, hopefully that'll fix it. I ground my pillar lower on the rear under the trigger guard.
If you had it done by a gunsmith, probably best to send it back.
