I would guess something related to the yoke and the cylinder assembly as a result of the plating. Cylinder binding on the barrel of the yoke, or not enough end shake for the cylinder assebly to rotate properly when closed. Plating thickness can significantly change the gauges inside the components.
The yoke could also be slightly bent, which would cause a variety of issues, including binding on the center pin when the cylinder is closed.

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Ret. LE, FA Instr, S&W Armorer