TBN is 4.4.... so oxidation isn't from acidification.
"Oxidation stability is a chemical reaction that occurs with a combination of the lubricating oil and oxygen. The rate of oxidation is accelerated by high temperatures, water, acids and catalysts such as copper. ."
Do you by chance have an oil cooler that's made out of copper?
Iron is very low for 10k miles.
Someone here once said if TAN is high, then tin and copper track proportionally. So I doubt that your tan has crossed the TBN number.
"The rate of oxidation increases with time. The service life of a lubricant is also reduced with increases in temperature. Oxidation will lead to an increase in the oil's viscosity and deposits of varnish and sludge."
And yet the oil is at 12.2cst @ 100c... Where virgin is around 12.9cst.