1. Common sense (understanding the minting process) 2. Blakesley Effect (look up) 3. Blakesley Effect (look up) It isn't necessary to start a poll on your thread. Chris PS. Welcome to the neighborhood!
Post a larger photo of both sides of the center coin, and the edge of the missing portion. This may be a straight clip in spite of the strike on the opposite side.
I know you are a new member. Maybe new at trying to find error coins. But we do not call them factory defects. Mint Errors is the proper term.
Why anyone would do that to coins escapes me. But we get plenty examples of the work of busy little hands. Wonder sometimes if brains are involved at all.