My suggestion is to start by Checking "Metal Function":

With the Krag action out of its Stock, the action "cocked", and the Safety applied, you should be able to pull the trigger so the sear will clear the 'cocking-piece.

The Safety should continue to hold the Striker in the 'cocked' position.

When released, the Trigger/Sear assembly should move fully back into its original position.
If the Safety is moved to the 'off' position, the sear should be able to fully engage the cocking-piece.

If metal has been removed from the contact surfaces of the Safety and Cocking-Piece Rod, it may allow the striker mechanism to move forward slightly when the trigger is pulled (with Safety applied).
This could block the Trigger/Sear from returning to engage the Cocking-Piece.

(My understanding of things):

The Krag Safety-Lever, when moved to the "Safe" position, slightly retracts the striker-rod and locks the bolt closed.

This allows for free movement of the trigger/sear.

If the trigger is pulled and the striker-rod is not slightly retracted, the trigger/sear can 'hang-up' on it (in a 'false' position) and not return to its raised position.
 
If this happens, the Striker will release ('Fire'), when the Safety is rotated back to the "Off" position.

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