I had a P0300 code for random cylinders’ misfire for a couple weeks now. Today I went to check the spark plugs and all six plugs’ electrode had worn down badly. They were on the car for a little less than 40,000 miles. They are supposedly Denso Iridium in Toyota packaging from EBAY.
Wow, that's terrible and unfortunate. Here was a thread on how to spot fake ones, and from the official Denso PDF in case you haven't seen them before.