That is bizarre.
When you say "magnetic" do you mean the particles themselves are magnetized ? not just attracted to a magnet like iron filings ?
I would find the oil bottle you filled the engine up with and cut it open , see if your new oil was contaminated in any way.
I cant imagine where "magnetic" particles could come from, there is nothing in the engine that is magnetic.
The only thing may be some thing like a magnetic sump plug if it had one, but the magnetism should hold that together.
Very strange.
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