+1 on the ring end gap - that'd be my chief suspicion. It'd run fine until you started putting more load on it, then the ring would bind, start grabbing, and break. A ring upside-down could also explain it (incidentally, one fringe benefit of Wossner pistons is I don't think it's possible to get the piston in with the ring upside-down). Also, Kimpex may be the same thing as SPI and maybe another brand or two. If it's made in Taiwan, it probably is, and I hear they can be a decent piston. Probably not what I'd pick though. Whatever the case, It's definitely a bummer to have a new top end go nowhere like this...