With the trigger at rest, pull the hammer back until the hammer's disco sear and the disco sear are as close as they can get, then take a photo. The distance between the two should be around .003, and if the gap is larger than this, the disco will need to be retimed to close the gap (material removed from the bottom/front of the disco where it rides on the top of the hammer which cams the disco father forward to retard the reset release).
Simple put, it could be a combo of the gap being too large (advanced hammer release on reset), and you just dancing the trigger a short distance with it doubling the rifle/releasing the hammer off the disco and it riding it down with the carrier (released before the bolt had fully locked and the unlocked bolt preventing primer ignition).
Myself, I like the set the disco release just before the trigger comes back to rest (read .001 gap). This prevents the operator from accidentally bumping the rifle since the trigger must be fully released before the hammer can reset back to the primary sear. And, since I do stone the hammer sears to take out the unneeded creep, it insures that the trigger sear is in the correct position to retain the hammer on release, and not allow it to bounce past to fire the rifle (fire on trigger release).