P0420 b1s2 following b1s1, b1s1 has different peaks than b2s1

2018 Chevy Traverse v6, P0420, not using oil, 62k, light city driving only, repeat P0420, no other codes.
fuel trims look good
oil changes are factory and oil looks ok proper level.
Antifreeze over flow tank is lower by 3/8 inch but no indicated leaks.
New converter installed
The b1s1, b1s2 voltages and peaks do not look the same as b2s1, b2s2
The b1s2 looks good cold and starts the same as b2s2.
It will flatline at first then later start intermittent following b1s1 sine wave.
Is this a bad sensor?
Is there a leak somewhere? I have inspected and sprayed quite a bit. No result yet.
Air filter is STP.
Found bolt on air filter box stripped head. Just below the plug for the MAS airflow sensor. I repaired the bolt. Found a bit of filter edge in that. was dusted.