Thanks, this is a very interesting read.
My wife purchased new an '01 Lexus RX300(1MZFE/3.0L V6) with this exact issue. I could never nail it down. I replaced A/F sensors from year 2 til year 15 when we finally sold the SUV. I called her RX a "CEL HOUND" & an "A/F SENSOR EATER".
Although the vehicle was reliable overall, it caused me some headaches with the CEL's and the A/F sensors over the 15 yrs we owned it.
I would get a code for one of the A/F sensors, so I'd replace it. All was good!
Then 2-3 weeks later, the car would trigger another CEL. At that time, it would be the other A/F sensor. So I'd replace that sensor. All was good for ~ 2-3 yrs!
Sometimes when I'd disconnect/reconnect the battery, the CEL would appear. I'd clear it and wouldn't see the CEL for a year or so. WHAT's Going ON?
Then the process would start all over again!