My call - (not an A&P but a mech engr). That it keeps producing metal
(really how much though) makes me wonder.

I can't imagine this to be simple cylinder corrosion products. It all
depends on what you find, but it sure sounds to me like a cam failure.
The next question is why, on a nearly new engine.

Maybe you could get by with just removing the four rocker box covers &
see if the valve travels are still equal using a dial indicator.

If they are equal travel, it could be an oil pump or other accessory
gear.

If they are not equal, that would suggest a good choice and location to
remove a cylinder & look at that cam lobe system. Two of the cam lobes
are doubled up so that they each drive two intake valves on opposite
sides of the engine. These might be the most likely cam lobes to
fail, with the failure probably initiating on the RH side if it is
cold-start related.

Another possibility is a scored cylinder. If it is from cold start
damage, it will probably be worse on the top right side of the engine.
You might be able to see this with a light thru the top spark plug hole
while looking thru the bottom hole. Do this in a dark area. Maybe
your mechanic has a borescope alternate.

Assuming this engine has a full flow filter (not just a screen), the
condition of a typical rod bearing could be determined after a cylinder
removal. If it has only a screen, the bearings will almost certainly
be contaminated.

If there is camshaft or lifter debris embedded in the con rod big end
journal, I'd want to stop any further operation in hopes of at least
saving the crankshaft from further damage. Any camshaft wear debris is
going to be very hard & just might have the potential of scratching the
nitrided crankshaft. If any cam lobe is worn down, it isn't going to
heal itself - it's just going to create more metal.

Let us know what you find.