I was thinking about this problem a little bit. For right function of cat, there must be fuel mixture ok in engine or there will be problem. Fuel mixture is control by pre-cat o2 sensor.
And data from pre-cat o2 sensor are little bit strange (from your csv file).
The lower limit is only cca 0,24V and should be cca 0,1-0,15V.
And also when after cat o2 sensor reached 0V, pre-cat o2 sensor reached only 0,1V - marked on att. image.
You can try to do this test:
on 5th gear, speed cca 50mph, then full throttle up to 90mph, then release throttle and soft breaking and save rpm, o2 sensors data, to see this:
http://merkur_sound.sweb.cz/lambda2a.png
If the pre-cat o2 sensor will not reach 0V, like in my car, then problem is probably in this sensor.