I had pretty much the same thing happen with my 625-2. The threaded post simply sheared off. I found the parts on the ground and upon examination figured there must have been a structural flaw in the post. It was very apparent there was a crack in the metal causing it to shear flush with the surface of the bolt.

I only shoot mild loads so I wasn’t punishing my gun and even if I had been shooting heavy loads there’s no stress on that part.

I called Smith and they issued a shipping label and within a couple of weeks I had it back as good as new.