Look at the oil routing in the pic. There is no way for those pieces to get into the oil pan except thru the bypass hole from the oil filter. The oil galleys are only 1/2" in diameter, even the drain back holes in the heads are to small for the pieces to pass thru if they got in the oil fill spout. The oil pump being a gear pump is capable of pumping a very Hi pressure, it can't be completely blocked, the pressure has to be going back into the pan thru the oil pressure relief hole. I would say those pieces were in the oil cooler header when you changed the oil cooler, it's possible that the oil galley port is partially blocked.
I would pull the oil cooler and check for more pieces and see if the oil bypass is stuck open.
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